Resonant filter for solid state rf impedance matching network

ABSTRACT

In one embodiment, an RF impedance matching circuit includes at least one electronically variable capacitor (EVC) comprising discrete fixed capacitors. Each fixed capacitor has a corresponding switching circuit for switching in and out the fixed capacitor to alter a total capacitance of the EVC. Each switching circuit includes a diode operably coupled to the fixed capacitor to cause the switching in and out of the fixed capacitor, the diode being a PIN diode or an NIP diode. Each switching circuit further includes a driver circuit operably coupled to the diode, and a resonant filter positioned between the driver circuit and the diode. The resonant filter includes an inductor and a capacitor coupled in parallel.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation in part of U.S. patentapplication Ser. No. 17/363,207, filed Jun. 30, 2021, which is acontinuation in part of U.S. patent application Ser. No. 17/111,743,filed Dec. 4, 2020, which is a continuation in part of U.S. patentapplication Ser. No. 16/935,643, filed Jul. 22, 2020, which is acontinuation in part of U.S. patent application Ser. No. 16/926,002,filed Jul. 10, 2020, which is a continuation in part of U.S. patentapplication Ser. No. 16/839,424, filed Apr. 3, 2020, which is acontinuation of U.S. patent application Ser. No. 16/804,324, filed Feb.28, 2020, which is a continuation in part of U.S. patent applicationSer. No. 16/685,698, filed Nov. 15, 2019, which is a continuation inpart of U.S. patent application Ser. No. 16/592,453, filed Oct. 3, 2019,which is a continuation in part of U.S. patent application Ser. No.16/524,805, filed Jul. 29, 2019, which is a continuation in part of U.S.patent application Ser. No. 16/502,656, filed Jul. 3, 2019, which is acontinuation in part of U.S. patent application Ser. No. 16/029,742,filed Jul. 9, 2018, which claims the benefit of U.S. Provisional PatentApplication No. 62/530,446, filed Jul. 10, 2017. U.S. patent applicationSer. No. 16/502,656 further claims the benefit of U.S. ProvisionalPatent Application No. 62/693,625, filed Jul. 3, 2018.

U.S. patent application Ser. No. 16/524,805 further claims the benefitof U.S. Provisional Patent Application No. 62/711,141, filed Jul. 27,2018. U.S. patent application Ser. No. 16/592,453 further claims thebenefit of U.S. Provisional Patent Application No. 62/741,073, filedOct. 4, 2018, and U.S. Provisional Patent Application No. 62/782,915,filed Dec. 20, 2018. U.S. patent application Ser. No. 16/685,698 furtherclaims the benefit of U.S. Provisional Patent Application No.62/767,587, filed Nov. 15, 2018. U.S. patent application Ser. No.16/804,324 further claims the benefit of U.S. Provisional PatentApplication No. 62/812,019, filed Feb. 28, 2019, U.S. Provisional PatentApplication No. 62/812,025, filed Feb. 28, 2019, and U.S. ProvisionalPatent Application No. 62/812,047, filed Feb. 28, 2019. U.S. patentapplication Ser. No. 16/926,002 further claims the benefit of U.S.Provisional Patent Application No. 62/873,370, filed Jul. 12, 2019. U.S.patent application Ser. No. 16/935,643 further claims the benefit ofU.S. Provisional Patent Application No. 62/876,998, filed Jul. 22, 2019,and U.S. Provisional Patent Application No. 63/004,682, filed Apr. 3,2020. U.S. patent application Ser. No. 17/111,743 further claims thebenefit of U.S. Provisional Patent Application No. 62/943,838, filedDec. 5, 2019. U.S. patent application Ser. No. 17/363,207 further claimsthe benefit of U.S. Provisional Patent Application No. 63/059,229, filedJul. 31, 2020. The present application further claims the benefit ofU.S. Provisional Patent Application No. 63/177,005, filed Apr. 20, 2021.The disclosures of the foregoing references are incorporated herein byreference in their entireties.

BACKGROUND

The semiconductor device fabrication process uses plasma processing atdifferent stages of fabrication to make a semiconductor device such as amicroprocessor, a memory chip, or another integrated circuit or device.Plasma processing involves energizing a gas mixture by imparting energyto the gas molecules by the introduction of RF (radio frequency) energyinto the gas mixture. This gas mixture is typically contained in avacuum chamber, also called a plasma chamber, and the RF energy isintroduced through electrodes or other means in the chamber. In atypical plasma process, the RF generator generates power at the desiredRF frequency and power, and this power is transmitted through the RFcables and networks to the plasma chamber.

To provide efficient transfer of power from the RF generator to theplasma chamber, an RF matching network is positioned between the RFgenerator and the plasma chamber. The purpose of the RF matching networkis to transform the plasma impedance to a value suitable for the RFgenerator. In many cases, particularly in the semiconductor fabricationprocesses, the RF power is transmitted through 50 Ohm coaxial cables andthe system impedance (output impedance) of the RF generators is also 50Ohm. On the other hand, the impedance of the plasma, driven by the RFpower, varies. The impedance on the input side of the RF matchingnetwork must be transformed to non-reactive 50 Ohm (i.e., 50+j0) formaximum power transmission. RF matching network perform this task ofcontinuously transforming the plasma impedance to 50 Ohm for the RFgenerator.

A typical RF matching network is composed of variable capacitors and amicroprocessor-based control circuit to control the capacitors. Thevalue and size of the variable capacitors are influenced by the powerhandling capability, frequency of operation, and impedance range of theplasma chamber. The predominant variable capacitor in use in RF matchingnetworks is the vacuum variable capacitor (VVC). The VVC is anelectromechanical device, consisting of two concentric metallic ringsthat move in relation to each other to change the capacitance. Incomplex semiconductor processes, where the impedance changes are veryrapid, the rapid and frequent movements put stresses on the VVC leadingto their failures. VVC-based RF matching networks are one of the lastelectromechanical components in the semiconductor fabrication process.

As semiconductor devices shrink in size and become more complex,however, the feature geometries become very small. As a result, theprocessing time to fabricate these features becomes small, typically inthe 5-6 second range. Current RF matching networks take 1-2 seconds totune the process and this results in unstable process parameters for asignificant portion of the process time. Electronically variablecapacitor (EVC) technology (see, e.g., U.S. Pat. No. 7,251,121,incorporated herein by reference in its entirety) enables a reduction inthis semiconductor processing tune time from 1-2 seconds to less than500 microseconds. EVC-based matching networks are a type of solid statematching network. Their decreased tune time greatly increases theavailable stable processing time, thereby improving yield andperformance.

While EVC technology is known, it has yet to be developed into anindustry-accepted replacement for VVCs. Because an EVC is purely anelectronic device, an EVC is not a one-for-one replacement for a VVC inan RF matching network. Further advancements are therefore needed tomore fully take advantage of using EVCs as part of an RF matchingnetwork. One area where further advancement is needed is in quickly andreliably switching the EVC's fixed capacitors in and out.

BRIEF SUMMARY

The present disclosure may be directed to an RF impedance matchingcircuit comprising an RF input configured to operably couple to an RFsource providing an RF signal; an RF output configured to operablycouple to a plasma chamber; at least one electronically variablecapacitor (EVC) comprising discrete fixed capacitors, each fixedcapacitor of each EVC having a corresponding switching circuit forswitching in and out the fixed capacitor to alter a total capacitance ofthe EVC; and a control circuit configured to cause the switching in andout of the fixed capacitors of each EVC to enable an impedance match;wherein each switching circuit for each fixed capacitor of each EVCcomprises a diode operably coupled to the fixed capacitor to cause theswitching in and out of the fixed capacitor, the diode being a PIN diodeor an NIP diode; a driver circuit operably coupled to the diode; and aresonant filter positioned between the driver circuit and the diode, theresonant filter comprising an inductor and a capacitor coupled inparallel.

In another aspect, a method of matching an impedance comprises couplingan RF input of a matching circuit to an RF source; coupling an RF outputof the matching circuit to a plasma chamber, wherein the matchingcircuit comprises at least one electronically variable capacitor (EVC)comprising discrete fixed capacitors, each fixed capacitor of each EVChaving a corresponding switching circuit for switching in and out thefixed capacitor to alter a total capacitance of the EVC; and a controlcircuit configured to cause the switching in and out of the fixedcapacitors of each EVC to enable an impedance match; wherein eachswitching circuit for each fixed capacitor of each EVC comprises a diodeoperably coupled to the fixed capacitor to cause the switching in andout of the fixed capacitor, the diode being a PIN diode or an NIP diode;a driver circuit operably coupled to the diode; and a resonant filterpositioned between the driver circuit and the diode, the resonant filtercomprising an inductor and a capacitor coupled in parallel; and matchingan impedance by at least one of the switching circuits of the at leastone EVC switching in or out its corresponding fixed capacitor to alter atotal capacitance of the EVC.

In another aspect, a semiconductor processing tool comprises a plasmachamber configured to deposit a material onto a substrate or etch amaterial from the substrate; and an impedance matching circuit operablycoupled to the plasma chamber, the matching circuit comprising theaforementioned components.

In another aspect, a method of fabricating a semiconductor comprisesplacing a substrate in a plasma chamber configured to deposit a materiallayer on the substrate or etch a material layer from the substrate;energizing plasma within the plasma chamber by coupling RF power from anRF source to the plasma chamber to perform the deposition or etching;and while energizing the plasma, carrying out an impedance match by animpedance matching circuit coupled between the plasma chamber and the RFsource, the matching circuit comprising the aforementioned components.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a block diagram of an embodiment of a semiconductor processingsystem;

FIG. 2 is a block diagram of an embodiment of a semiconductor processingsystem having an L-configuration matching network;

FIG. 3 is a block diagram of an embodiment of a semiconductor processingsystem having a pi-configuration matching network;

FIG. 4 is a block diagram of an embodiment of an electronic circuit forproviding a variable capacitance using an electronically variablecapacitor having two capacitor arrays;

FIG. 5 is a block diagram of an embodiment of a variable capacitancesystem for switching in and out discrete capacitors of an electronicallyvariable capacitor;

FIG. 6 is a flow chart showing an embodiment of a process for matchingan impedance by altering a variable capacitance;

FIG. 7 is a flow chart showing another embodiment of a process formatching an impedance using a parameter matrix to alter a variablecapacitance;

FIG. 8 is a flow chart showing another embodiment of a process formatching an impedance where a frequency of an RF source is also altered;and

FIG. 9 is a flow chart showing another embodiment of a process formatching an impedance where capacitor switching can be restricted.

FIG. 10 is a flow chart showing an embodiment of a process for matchingan impedance using a lookup table to alter an EVC configuration and anRF source frequency.

FIG. 11 is a flow chart showing an embodiment of a process for matchingan impedance where capacitance and frequency are adjusted independently.

FIG. 12 is a schematic of an embodiment of a matching network having afrequency-sensitive circuit responsive to frequency adjustments.

FIG. 13 is a portion of a Smith chart showing simulation results for aone-dimensional match.

FIG. 14 is flow chart of an embodiment of a process for impedancematching when the RF input signal has multi-level power setpointsaccording to one embodiment.

FIG. 15 is a graph showing the pulse levels and timing ofparameter-related value determinations according to the embodiment ofFIG. 14.

FIG. 16 is a block diagram of a switching circuit for an electronicallyvariable capacitor of a matching network according to one embodiment.

FIG. 17 is a flow chart for performing diagnostics on a matching networkaccording to one embodiment.

FIG. 18 is a flow chart for performing a driver test on a matchingnetwork according to one embodiment.

FIG. 19 is a flow chart for a level-to-level impedance matching methodusing pre-pulse capacitor switching according to one embodiment.

FIG. 20 is a flow chart for an impedance matching method where parametervalues are assigned to different activities according to one embodiment.

FIG. 21 is a flow chart for a level-to-level impedance matching methodwhere a pulse level is prioritized according to one embodiment.

FIG. 22 is a flow chart of an impedance matching method where switchingis limited based on a blocking voltage value according to oneembodiment.

FIG. 23 is a flow chart of an impedance matching method for finding thebest capacitor position for impedance matching where switching isrestricted, according to one embodiment.

FIG. 24 is a flow chart of an impedance matching method that alsocontrols the power delivered to the plasma chamber, according to oneembodiment.

FIG. 25 is a flow chart of a method of using an impedance matchingnetwork to determine a plasma chamber characteristic, according to oneembodiment.

FIG. 26 is a flow chart of a method of manufacturing a semiconductorusing a learning model, according to one embodiment.

FIG. 27 is a block diagram of an RF generator, according to oneembodiment.

FIG. 28 is a transient response of an RF generator, according to oneembodiment.

FIG. 29 is a flow chart of a method of matching an impedance using amatching network in coordinated operation with an RF generator,according to one embodiment.

FIG. 30 is a block diagram of a switching circuit for an electronicallyvariable capacitor of a matching network according to one embodiment.

DETAILED DESCRIPTION

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention orinventions. The description of illustrative embodiments is intended tobe read in connection with the accompanying drawings, which are to beconsidered part of the entire written description. In the description ofthe exemplary embodiments disclosed herein, any reference to directionor orientation is merely intended for convenience of description and isnot intended in any way to limit the scope of the present inventions.The discussion herein describes and illustrates some possiblenon-limiting combinations of features that may exist alone or in othercombinations of features. Furthermore, as used herein, the term “or” isto be interpreted as a logical operator that results in true wheneverone or more of its operands are true. Furthermore, as used herein, thephrase “based on” is to be interpreted as meaning “based at least inpart on,” and therefore is not limited to an interpretation of “basedentirely on.”

Features of the present inventions may be implemented in software,hardware, firmware, or combinations thereof. The computer programsdescribed herein are not limited to any particular embodiment, and maybe implemented in an operating system, application program, foregroundor background processes, driver, or any combination thereof. Thecomputer programs may be executed on a single computer or serverprocessor or multiple computer or server processors.

Processors described herein may be any central processing unit (CPU),microprocessor, micro-controller, computational, or programmable deviceor circuit configured for executing computer program instructions (e.g.,code). Various processors may be embodied in computer and/or serverhardware of any suitable type (e.g., desktop, laptop, notebook, tablets,cellular phones, etc.) and may include all the usual ancillarycomponents necessary to form a functional data processing deviceincluding without limitation a bus, software and data storage such asvolatile and non-volatile memory, input/output devices, graphical userinterfaces (GUIs), removable data storage, and wired and/or wirelesscommunication interface devices including Wi-Fi, Bluetooth, LAN, etc.

Computer-executable instructions or programs (e.g., software or code)and data described herein may be programmed into and tangibly embodiedin a non-transitory computer-readable medium that is accessible to andretrievable by a respective processor as described herein whichconfigures and directs the processor to perform the desired functionsand processes by executing the instructions encoded in the medium. Adevice embodying a programmable processor configured to suchnon-transitory computer-executable instructions or programs may bereferred to as a “programmable device”, or “device”, and multipleprogrammable devices in mutual communication may be referred to as a“programmable system.” It should be noted that non-transitory“computer-readable medium” as described herein may include, withoutlimitation, any suitable volatile or non-volatile memory includingrandom access memory (RAM) and various types thereof, read-only memory(ROM) and various types thereof, USB flash memory, and magnetic oroptical data storage devices (e.g., internal/external hard disks, floppydiscs, magnetic tape CD-ROM, DVD-ROM, optical disk, ZIP™ drive, Blu-raydisk, and others), which may be written to and/or read by a processoroperably connected to the medium.

In certain embodiments, the present invention may be embodied in theform of computer-implemented processes and apparatuses such asprocessor-based data processing and communication systems or computersystems for practicing those processes. The present invention may alsobe embodied in the form of software or computer program code embodied ina non-transitory computer-readable storage medium, which when loadedinto and executed by the data processing and communications systems orcomputer systems, the computer program code segments configure theprocessor to create specific logic circuits configured for implementingthe processes.

As used throughout, ranges are used as shorthand for describing each andevery value that is within the range. Any value within the range can beselected as the terminus of the range. In addition, all references citedherein are hereby incorporated by referenced in their entireties. In theevent of a conflict in a definition in the present disclosure and thatof a cited reference, the present disclosure controls.

In the following description, where circuits are shown and described,one of skill in the art will recognize that, for the sake of clarity,not all peripheral circuits or components are shown in the figures ordescribed in the description. Further, the terms “couple” and “operablycouple” can refer to a direct or indirect coupling of two components ofa circuit.

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention orinventions. The description of illustrative embodiments is intended tobe read in connection with the accompanying drawings, which are to beconsidered part of the entire written description. In the description ofthe exemplary embodiments disclosed herein, any reference to directionor orientation is merely intended for convenience of description and isnot intended in any way to limit the scope of the present invention.Relative terms such as “lower,” “upper,” “horizontal,” “vertical,”“above,” “below,” “up,” “down,” “left,” “right,” “top,” “bottom,”“front” and “rear” as well as derivatives thereof (e.g., “horizontally,”“downwardly,” “upwardly,” etc.) should be construed to refer to theorientation as then described or as shown in the drawing underdiscussion. These relative terms are for convenience of description onlyand do not require that the apparatus be constructed or operated in aparticular orientation unless explicitly indicated as such. Terms suchas “attached,” “affixed,” “connected,” “coupled,” “interconnected,”“secured” and other similar terms refer to a relationship whereinstructures are secured or attached to one another either directly orindirectly through intervening structures, as well as both movable orrigid attachments or relationships, unless expressly describedotherwise. The discussion herein describes and illustrates some possiblenon-limiting combinations of features that may exist alone or in othercombinations of features. Furthermore, as used herein, the term “or” isto be interpreted as a logical operator that results in true wheneverone or more of its operands are true. Furthermore, as used herein, thephrase “based on” is to be interpreted as meaning “based at least inpart on,” and therefore is not limited to an interpretation of “basedentirely on.”

As used throughout, ranges are used as shorthand for describing each andevery value that is within the range. Any value within the range can beselected as the terminus of the range. In addition, all references citedherein are hereby incorporated by referenced in their entireties. In theevent of a conflict in a definition in the present disclosure and thatof a cited reference, the present disclosure controls.

Semiconductor Processing System

Referring to FIG. 1, a semiconductor device processing system 5utilizing an RF generator 15 is shown. The system 85 includes an RFgenerator 15 and a semiconductor processing tool 86. The semiconductorprocessing tool 86 includes a matching network 11 and a plasma chamber19. In other embodiments, the generator 15 or other power source canform part of the semiconductor processing tool.

The semiconductor device can be a microprocessor, a memory chip, orother type of integrated circuit or device. A substrate 27 can be placedin the plasma chamber 19, where the plasma chamber 19 is configured todeposit a material layer onto the substrate 27 or etch a material layerfrom the substrate 27. Plasma processing involves energizing a gasmixture by imparting energy to the gas molecules by introducing RFenergy into the gas mixture. This gas mixture is typically contained ina vacuum chamber (the plasma chamber 19), and the RF energy is typicallyintroduced into the plasma chamber 19 through electrodes. Thus, theplasma can be energized by coupling RF power from an RF source 15 intothe plasma chamber 19 to perform deposition or etching.

In a typical plasma process, the RF generator 15 generates power at aradio frequency—which is typically within the range of 3 kHz and 300GHz—and this power is transmitted through RF cables and networks to theplasma chamber 19. In order to provide efficient transfer of power fromthe RF generator 15 to the plasma chamber 19, an intermediary circuit isused to match the fixed impedance of the RF generator 15 with thevariable impedance of the plasma chamber 19. Such an intermediarycircuit is commonly referred to as an RF impedance matching network, ormore simply as an RF matching network. The purpose of the RF matchingnetwork 11 is to transform the variable plasma impedance to a value thatmore closely matches the fixed impedance of the RF generator 15.Commonly owned U.S. patent application Ser. No. 14/669,568, thedisclosure of which is incorporated herein by reference in its entirety,provides an example of such a matching network.

Matching Network

FIG. 2 is a block diagram of an embodiment of a semiconductor processingsystem 85 having a processing tool 86 that includes an L-configurationRF impedance matching network 11. The matching network 11 has an RFinput 13 connected to an RF source 15 and an RF output 17 connected to aplasma chamber 19. An RF input sensor 21 can be connected between the RFimpedance matching network 11 and the RF source 15. An RF output sensor49 can be connected between the RF impedance matching network 11 and theplasma chamber 19 so that the RF output from the impedance matchingnetwork, and the plasma impedance presented by the plasma chamber 19,may be monitored. Certain embodiments may include only one of the inputsensor 21 and the output sensor 49. The functioning of these sensors 21,49 are described in greater detail below.

As discussed above, the RF impedance matching network 11 serves to helpmaximize the amount of RF power transferred from the RF source 15 to theplasma chamber 19 by matching the impedance at the RF input 13 to thefixed impedance of the RF source 15. The matching network 11 can consistof a single module within a single housing designed for electricalconnection to the RF source 15 and plasma chamber 19. In otherembodiments, the components of the matching network 11 can be located indifferent housings, some components can be outside of the housing,and/or some components can share a housing with a component outside thematching network.

As is known in the art, the plasma within a plasma chamber 19 typicallyundergoes certain fluctuations outside of operational control so thatthe impedance presented by the plasma chamber 19 is a variableimpedance. Since the variable impedance of the plasma chamber 19 cannotbe fully controlled, and an impedance matching network may be used tocreate an impedance match between the plasma chamber 19 and the RFsource 15. Moreover, the impedance of the RF source 15 may be fixed at aset value by the design of the particular RF source 15. Although thefixed impedance of an RF source 15 may undergo minor fluctuations duringuse, due to, for example, temperature or other environmental variations,the impedance of the RF source 15 is still considered a fixed impedancefor purposes of impedance matching because the fluctuations do notsignificantly vary the fixed impedance from the originally set impedancevalue. Other types of RF source 15 may be designed so that the impedanceof the RF source 15 may be set at the time of, or during, use. Theimpedance of such types of RF sources 15 is still considered fixedbecause it may be controlled by a user (or at least controlled by aprogrammable controller) and the set value of the impedance may be knownat any time during operation, thus making the set value effectively afixed impedance.

The RF source 15 may be an RF generator of a type that is well-known inthe art, and generates an RF signal at an appropriate frequency andpower for the process performed within the plasma chamber 19. The RFsource 15 may be electrically connected to the RF input 13 of the RFimpedance matching network 11 using a coaxial cable, which for impedancematching purposes would have the same fixed impedance as the RF source15.

The plasma chamber 19 includes a first electrode 23 and a secondelectrode 25, and in processes that are well known in the art, the firstand second electrodes 23, 25, in conjunction with appropriate controlsystems (not shown) and the plasma in the plasma chamber, enable one orboth of deposition of materials onto a substrate 27 and etching ofmaterials from the substrate 27.

In the exemplified embodiment, the RF impedance matching network 11includes a series variable capacitor 31, a shunt variable capacitor 33,and a series inductor 35 to form an ‘L’ type matching network. The shuntvariable capacitor 33 is shown shunting to a reference potential, inthis case ground 40, between the series variable capacitor 31 and theseries inductor 35, and one of skill in the art will recognize that theRF impedance matching network 11 may be configured with the shuntvariable capacitor 33 shunting to a reference potential at the RF input13 or at the RF output 17.

Alternatively, the RF impedance matching network 11 may be configured inother matching network configurations, such as a ‘T’ type configurationor a ‘Π’ or ‘pi’ type configuration, as will be shown in FIG. 3. Incertain embodiments, the variable capacitors and the switching circuitdescribed below may be included in any configuration appropriate for anRF impedance matching network.

In the exemplified embodiment, each of the series variable capacitor 31and the shunt variable capacitor 33 may be an electronic variablecapacitor (EVC), as described in U.S. Pat. No. 7,251,121, the EVC beingeffectively formed as a capacitor array formed by a plurality ofdiscrete capacitors. The series variable capacitor 31 is coupled inseries between the RF input 13 and the RF output 17 (which is also inparallel between the RF source 15 and the plasma chamber 19). The shuntvariable capacitor 33 is coupled in parallel between the RF input 13 andground 40. In other configurations, the shunt variable capacitor 33 maybe coupled in parallel between the RF output 19 and ground 40. Otherconfigurations may also be implemented without departing from thefunctionality of an RF matching network. In still other configurations,the shunt variable capacitor 33 may be coupled in parallel between areference potential and one of the RF input 13 and the RF output 19.

The series variable capacitor 31 is connected to a series RF choke andfilter circuit 37 and to a series driver circuit 39. Similarly, theshunt variable capacitor 33 is connected to a shunt RF choke and filtercircuit 41 and to a shunt driver circuit 43. Each of the series andshunt driver circuits 39, 43 are connected to a control circuit 45,which is configured with an appropriate processor and/or signalgenerating circuitry to provide an input signal for controlling theseries and shunt driver circuits 39, 43. A power supply 47 is connectedto each of the RF input sensor 21, the series driver circuit 39, theshunt driver circuit 43, and the control circuit 45 to provideoperational power, at the designed currents and voltages, to each ofthese components. The voltage levels provided by the power supply 47,and thus the voltage levels employed by each of the RF input sensor 21,the series driver circuit 39, the shunt driver circuit 43, and thecontrol circuit 45 to perform the respective designated tasks, is amatter of design choice. In other embodiments, a variety of electroniccomponents can be used to enable the control circuit 45 to sendinstructions to the variable capacitors. Further, while the drivercircuit and RF choke and filter are shown as separate from the controlcircuit 45, these components can also be considered as forming part ofthe control circuit 45.

In the exemplified embodiment, the control circuit 45 includes aprocessor. The processor may be any type of properly programmedprocessing device, such as a computer or microprocessor, configured forexecuting computer program instructions (e.g., code). The processor maybe embodied in computer and/or server hardware of any suitable type(e.g., desktop, laptop, notebook, tablets, cellular phones, etc.) andmay include all the usual ancillary components necessary to form afunctional data processing device including without limitation a bus,software and data storage such as volatile and non-volatile memory,input/output devices, graphical user interfaces (GUIs), removable datastorage, and wired and/or wireless communication interface devicesincluding Wi-Fi, Bluetooth, LAN, etc. The processor of the exemplifiedembodiment is configured with specific algorithms to enable matchingnetwork to perform the functions described herein.

With the combination of the series variable capacitor 31 and the shuntvariable capacitor 33, the combined impedances of the RF impedancematching network 11 and the plasma chamber 19 may be controlled, usingthe control circuit 45, the series driver circuit 39, the shunt drivercircuit 43, to match, or at least to substantially match, the fixedimpedance of the RF source 15.

The control circuit 45 is the brains of the RF impedance matchingnetwork 11, as it receives multiple inputs, from sources such as the RFinput sensor 21 and the series and shunt variable capacitors 31, 33,makes the calculations necessary to determine changes to the series andshunt variable capacitors 31, 33, and delivers commands to the seriesand shunt variable capacitors 31, 33 to create the impedance match. Thecontrol circuit 45 is of the type of control circuit that is commonlyused in semiconductor fabrication processes, and therefore known tothose of skill in the art. Any differences in the control circuit 45, ascompared to control circuits of the prior art, arise in programmingdifferences to account for the speeds at which the RF impedance matchingnetwork 11 is able to perform switching of the variable capacitors 31,33 and impedance matching.

Each of the series and shunt RF choke and filter circuits 37, 41 areconfigured so that DC signals may pass between the series and shuntdriver circuits 39, 43 and the respective series and shunt variablecapacitors 31, 33, while at the same time the RF signal from the RFsource 15 is blocked to prevent the RF signal from leaking into theoutputs of the series and shunt driver circuits 39, 43 and the output ofthe control circuit 45. The series and shunt RF choke and filtercircuits 37, 41 are of a type known to those of skill in the art.

FIG. 3 is a block diagram of an embodiment of a semiconductor processingsystem 85A having a pi-configuration matching network 11A, as opposed tothe L-configuration matching network of FIG. 2. For ease ofunderstanding, this figure omits the RF chokes and filters, drivercircuits, and power supplies of FIG. 2. Where FIG. 3 uses referencenumbers identical to those of FIG. 2, it is understood that the relevantcomponents can have features similar to those discussed with regard toFIG. 2.

The most significant difference between the L- and pi-configuration isthat the L-configuration utilizes a series capacitor 31 and shuntcapacitor 33, while the pi-configuration utilizes two shunt capacitors31A, 33A. Nevertheless, the control circuit can alter the capacitance ofthese shunt variable capacitors 31A, 33A to cause an impedance match.Each of these shunt variable capacitors 31A, 33A can be an EVC, asdiscussed above. They can be controlled by a choke, filter, and driversimilar to the methods discussed above with respect to FIG. 2.

EVC Capacitor Arrays

FIG. 4 shows an electronic circuit 650 for providing a variablecapacitance according to one embodiment. The circuit 650 utilizes an EVC651 that includes two capacitor arrays 651 a, 651 b. The first capacitorarray 651 a has a first plurality of discrete capacitors, each having afirst capacitance value. The second capacitor array 651 b has a secondplurality of discrete capacitors, each having a second capacitancevalue. The first capacitance value is different from the secondcapacitance value such that the EVC 651 can provide coarse and finecontrol of the capacitance produced by the EVC 651. The first capacitorarray and the second capacitor array are coupled in parallel between asignal input 613 and a signal output 630.

The first and second capacitance values can be any values sufficient toprovide the desired overall capacitance values for the EVC 651. In oneembodiment, the second capacitance value is less than or equal toone-half (½) of the first capacitance value. In another embodiment, thesecond capacitance value is less than or equal to one-third (⅓) of thefirst capacitance value. In yet another embodiment, the secondcapacitance value is less than or equal to one-fourth (¼) of the firstcapacitance value.

The electronic circuit 650 further includes a control circuit 645, whichcan have features similar to control circuit 45 discussed above. Thecontrol circuit 645 is operably coupled to the first capacitor array 651a and to the second capacitor array 651 b by a command input 629, thecommand input 629 being operably coupled to the first capacitor array651 a and to the second capacitor array 651 b. In the exemplifiedembodiment, the command input 629 has a direct electrical connection tothe capacitor arrays 651 a, 651 b, though in other embodiments thisconnection can be indirect. The coupling of the control circuit 645 tothe capacitor arrays 651 a, 651 b will be discussed in further detailbelow.

The control circuit 645 is configured to alter the variable capacitanceof the EVC 651 by controlling on and off states of (a) each discretecapacitor of the first plurality of discrete capacitors and (b) eachdiscrete capacitor of the second plurality of discrete capacitors. Asstated above, the control circuit 645 can have features similar to thosedescribed with respect to control circuit 45 of FIGS. 2-3. For example,the control circuit 645 can receive inputs from the capacitor arrays 651a, 651 b, make calculations to determine changes to capacitor arrays 651a, 651 b, and delivers commands to the capacitor arrays 651 a, 651 b foraltering the capacitance of the EVC 651. EVC 651 of FIG. 4 can include aplurality of electronic switches. Each electronic switch can beconfigured to activate and deactivate one or more discrete capacitors.

As with the control circuit 45 of FIGS. 2-3, the control circuit 645 canalso be connected to a driver circuit 639 and an RF choke and filtercircuit 637. The control circuit 645, driver circuit 639, and RF chokeand filter circuit 637 can have capabilities similar to those discussedwith regard to FIG. 2-3. In the exemplified embodiment, the drivercircuit 639 is operatively coupled between the control circuit 645 andthe first and second capacitor arrays 651 a, 651 b. The driver circuit639 is configured to alter the variable capacitance based upon a controlsignal received from the control circuit 645. The RF filter 637 isoperatively coupled between the driver circuit 639 and the first andsecond capacitor arrays 651 a, 651 b. In response to the control signalsent by the control unit 645, the driver circuit 639 and RF filter 637are configured to send a command signal to the command input 629. Thecommand signal is configured to alter the variable capacitance byinstructing at least one of the electronic switches to activate ordeactivate (a) at least one the discrete capacitors of the firstplurality of discrete capacitors or (b) at least one of the discretecapacitors of the second plurality of discrete capacitors.

In the exemplified embodiment, the driver circuit 639 is configured toswitch a high voltage source on or off in less than 15 μsec, the highvoltage source controlling the electronic switches of each of the firstand second capacitor arrays for purposes of altering the variablecapacitance. The EVC 651, however, can be switched by any of the meansor speeds discussed in the present application.

The control circuit 645 can be configured to calculate coarse and finecapacitance values to be provided by the respective capacitor arrays 651a, 651 b. In the exemplified embodiment, the control circuit 645 isconfigured to calculate a coarse capacitance value to be provided bycontrolling the on and off states of the first capacitor array 651 a.Further, the control circuit is configured to calculate a finecapacitance value to be provided by controlling the on and off states ofthe second capacitor array 651 b. In other embodiments, the capacitorarrays 651 a, 651 b can provide alternative levels of capacitance. Inother embodiments, the EVC can utilize additional capacitor arrays.

EVC 651 of FIG. 4 can be used in most systems requiring a varyingcapacitance. For example, EVC 651 can be used as the series EVC and/orshunt EVC in matching network 11 of FIG. 2, or as one or both of theshunt EVCs in matching network 11A of FIG. 3. It is often desired thatthe differences between the capacitance values allow for both asufficiently fine resolution of the overall capacitance of the circuitand a wide range of capacitance values to enable a better impedancematch at the input of a RF matching network, and EVC 651 allows this.

EVC 651 can also be used in a system or method for fabricating asemiconductor, a method for controlling a variable capacitance, and/or amethod of controlling an RF impedance matching network. Such methods caninclude altering at least one of the series variable capacitance and theshunt variable capacitance to the determined series capacitance valueand the shunt capacitance value, respectively. This altering can beaccomplishing by controlling, for each of the series EVC and the shuntEVC, on and off states of each discrete capacitor of each plurality ofdiscrete capacitors. In other embodiments, EVC 651 and circuit 650 canbe used in other methods and systems to provide a variable capacitance.

Switching in and Out Discrete Capacitors to Vary EVC Capacitance

As discussed above, an EVC is a type of variable capacitor that can usemultiple switches, each used to create an open or short circuit, withindividual series capacitors to change the capacitance of the variablecapacitor. The switches can be mechanical (such as relays) or solidstate (such as PIN diodes, transistors, or other switching devices). Thefollowing is a discussion of methods for setting up an EVC or othervariable capacitor to provide varying capacitances.

In what is sometimes referred to as an “accumulative setup” of an EVC orother variable capacitor, the approach to linearly increase thecapacitor value from the minimum starting point (where all switches areopen) is to incrementally increase the number of fine tune capacitorsthat are switched into the circuit. Once the maximum number of fine tunecapacitors is switched into circuit, a coarse tune capacitor is switchedin, and the fine tune capacitors are switched out. The process startsover with increasing the number of fine tune capacitors that areswitched into circuit, until all fine and coarse tune capacitors areswitched in, at which point another coarse tune capacitor is switched inand the fine tune capacitors are switched out. This process can continueuntil all the coarse and fine capacitors are switched in.

In this embodiment, all of the fine tune capacitors have the same or asubstantially similar value, and all the coarse tune capacitors have thesame or a substantially similar value. Further, the capacitance value ofone coarse tune capacitor about equals the combined capacitance value ofall fine tune capacitors plus an additional fine tune capacitor into thecircuit, thus enabling a linear increase in capacitance. Theembodiments, however, are not so limited. The fine tune capacitors (andcoarse capacitors) need not have the same or a substantially similarvalue. Further, the capacitance value of one coarse tune capacitor neednot equal the combined capacitance value of all fine tune capacitorsplus an additional fine tune capacitor. In one embodiment, the coarsecapacitance value and the fine capacitance value have a ratiosubstantially similar to 10:1. In another embodiment, the secondcapacitance value is less than or equal to one-half (½) of the firstcapacitance value. In another embodiment, the second capacitance valueis less than or equal to one-third (⅓) of the first capacitance value.In yet another embodiment, the second capacitance value is less than orequal to one-fourth (¼) of the first capacitance value.

An example of the aforementioned embodiment in an ideal setting would beif the fine tune capacitors were equal to 1 pF, and the coarse tunecapacitors were equal to 10 pF. In this ideal setup, when all switchesare open, the capacitance is equal to 0 pF. When the first switch isclosed, there is 1 pF in the circuit. When the second switch is closedthere is 2 pF in the circuit, and so on, until nine fine tune switchesare closed, giving 9 pF. Then, the first 10 pF capacitor is switchedinto circuit and the nine fine tune switches are opened, giving a totalcapacitance of 10 pF. The fine tune capacitors are then switched intocircuit from 11 pF to 19 pF. Another coarse tune capacitor can then beswitched into circuit and all fine tune capacitors can be switched outof circuit giving 20 pF. This process can be repeated until the desiredcapacitance is reached.

This can also be taken one step further. Using the previous example,having nine 1 pF capacitors and also nine 10 pF capacitors, the variablecapacitor circuit can have even larger values, 100 pF, to switch in andout of circuit. This would allow the previous capacitor array to go upto 99 pF, and then the 100 pF capacitor can be used for the nextincrement. This can be repeated further using larger increments, and canalso be used with any counting system. According to the accumulativesetup, increasing the total capacitance of a variable capacitor isachieved by switching in more of the coarse capacitors or more of thefine capacitors than are already switched in without switching out acoarse capacitor that is already switched in. Further, when the variabletotal capacitance is increased and the control circuit does not switchin more of the coarse capacitors than are already switched in, then thecontrol circuit switches in more fine capacitors than are alreadyswitched in without switching out a fine capacitor that is alreadyswitched in.

FIG. 5 is a schematic of a variable capacitance system 655 according toan accumulative setup. Where this figure uses reference numbersidentical to those of FIG. 4, it is understood that the relevantcomponents can have features similar to those discussed in FIG. 4. Thevariable capacitance system 655 comprises a variable capacitor 651 forproviding a varying capacitance. The variable capacitor 651 has an input613 and an output 630. The variable capacitor 651 includes a pluralityof discrete capacitors 653 operably coupled in parallel. The pluralityof capacitors 653 includes first (fine) capacitors 651 a and second(coarse) capacitors 651B. Further, the variable capacitor 651 includes aplurality of switches 661. Of the switches 661, one switch is operablycoupled in series to each of the plurality of capacitors to switch inand out each capacitor, thereby enabling the variable capacitor 651 toprovide varying total capacitances. The variable capacitor 651 has avariable total capacitance that is increased when discrete capacitors653 are switched in and decreased when the discrete capacitors 653 areswitched out.

The switches 661 can be coupled to switch driver circuits 639 fordriving the switches on and off. The variable capacitance system 655 canfurther include a control unit 645 operably coupled to the variablecapacitor 651. Specifically, the control unit 645 can be operablycoupled to the driver circuits 639 for instructing the driver circuits639 to switch one or more of the switches 661, and thereby turn one ormore of the capacitors 653 on or off. In one embodiment, the controlunit 645 can form part of a control unit that controls a variablecapacitor, such as a control unit that instructs the variable capacitorsof a matching network to change capacitances to achieve an impedancematch. The driver circuits 639 and control unit 645 can have featuressimilar to those discussed above with reference to FIG. 4, and thus canalso utilize an RF choke and filter as discussed above.

In one embodiment, the control circuit 645 is configured to determine adesired coarse capacitance for the coarse capacitors; determine adesired fine capacitance for the fine capacitors; and after calculatingthe desired coarse capacitance and the desired fine capacitance, alterthe total variable capacitance by switching in or out at least one ofthe fine capacitors; and switching in or out at least one of the coarsecapacitors. In other embodiments, coarse tuning and fine tuning canoccur at different stages.

In the exemplified embodiment, the first capacitors 651 a are finecapacitors each having a capacitance value substantially similar to afine capacitance value, and the second capacitors 651 b are coarsecapacitors each having a capacitance value substantially similar to acoarse capacitance value, the coarse capacitance value being greaterthan the fine capacitance value. For purposes of this application,capacitances and other values are considered to be substantially similarif one value is not 15 percent (15%) greater than or less than anothervalue.

The variable capacitance system 655 can form part of an impedancematching network, including but not limited to, the impedance matchingnetworks of FIGS. 1-3. The variable capacitance system can also formpart of a method for controlling an impedance matching network (such asthe impedance matching networks of FIGS. 1-3). The method can includeproviding the RF impedance matching network comprising determining anincreased total capacitance to be provided by one of the EVCs; andincreasing the variable total capacitance of the one EVC by switching inmore of the coarse capacitors or more of the fine capacitors than arealready switched in without switching out a coarse capacitor that isalready switched in. Further, the variable capacitance system can formpart of a method and system for fabricating a semiconductor (see FIGS.1-3).

Using the variable capacitance system discussed above with an impedancematching network can provide several advantages over other approaches.An alternative to the above approach would be to have all the capacitorvalues be different, with the first value equal to the minimum desiredchange in capacitance. Then each successive capacitor value is increasedto double the change in capacitance from the previous up until themaximum desired capacitor value, when all capacitors are switched in.This approach can result in using less capacitors to switch in and outof circuit to achieve the same resolution and range. A potential problemwith this setup, however, is that, once the capacitor reaches a certainvalue, the voltage and/or current on that particular capacitor or thecurrent on the switch can be higher than the specification allows for.This forces the EVC to use multiple capacitors in parallel for eachswitch of lower value. This problem is particularly acute where highvoltages and/or currents are being used. The accumulative setupdiscussed above avoids putting this degree of stress on its capacitorsand switches by switching in additional capacitors, rather thanreplacing lower-capacitance capacitors with higher-capacitancecapacitors.

Determining Capacitance Values to Achieve Match

FIG. 6 is a flow chart showing a process 500A for matching an impedanceaccording to one embodiment. The matching network can include componentssimilar to those discussed above. In one embodiment, the matchingnetwork of FIG. 2 is utilized. In the first step of the exemplifiedprocess 500A of FIG. 6, an input impedance at the RF input 13 isdetermined (step 501A). The input impedance is based on the RF inputparameter detected by the RF input sensor 21 at the RF input 13. The RFinput sensor 21 can be any sensor configured to detect an RF inputparameter at the RF input 13. The input parameter can be any parametermeasurable at the RF input 13, including a voltage, a current, or aphase at the RF input 13. In the exemplified embodiment, the RF inputsensor 21 detects the voltage, current, and phase at the RF input 13 ofthe matching network 11. Based on the RF input parameter detected by theRF input sensor 21, the control circuit 45 determines the inputimpedance.

Next, the control circuit 45 determines the plasma impedance presentedby the plasma chamber 19 (step 502A). In one embodiment, the plasmaimpedance determination is based on the input impedance (determined instep 501A), the capacitance of the series EVC 31, and the capacitance ofthe shunt EVC 33. In other embodiments, the plasma impedancedetermination can be made using the output sensor 49 operably coupled tothe RF output, the RF output sensor 49 configured to detect an RF outputparameter. The RF output parameter can be any parameter measurable atthe RF output 17, including a voltage, a current, or a phase at the RFoutput 17. The RF output sensor 49 may detect the output parameter atthe RF output 17 of the matching network 11. Based on the RF outputparameter detected by the RF output sensor 21, the control circuit 45may determine the plasma impedance. In yet other embodiments, the plasmaimpedance determination can be based on both the RF output parameter andthe RF input parameter.

Once the variable impedance of the plasma chamber 19 is known, thecontrol circuit 45 can determine the changes to make to the variablecapacitances of one or both of the series and shunt EVCs 31, 33 forpurposes of achieving an impedance match. Specifically, the controlcircuit 45 determines a first capacitance value for the series variablecapacitance and a second capacitance value for the shunt variablecapacitance (step 503A). These values represent the new capacitancevalues for the series EVC 31 and shunt EVC 33 to enable an impedancematch, or at least a substantial impedance match. In the exemplifiedembodiment, the determination of the first and second capacitance valuesis based on the variable plasma impedance (determined in step 502A) andthe fixed RF source impedance.

Once the first and second capacitance values are determined, the controlcircuit 45 generates a control signal to alter at least one of theseries variable capacitance and the shunt variable capacitance to thefirst capacitance value and the second capacitance value, respectively(step 504A). This is done at approximately t=−5 μsec. The control signalinstructs the switching circuit to alter the variable capacitance of oneor both of the series and shunt EVCs 31, 33.

This alteration of the EVCs 31, 33 takes about 9-11 μsec total, ascompared to about 1-2 sec of time for an RF matching network using VVCs.Once the switch to the different variable capacitances is complete,there is a period of latency as the additional discrete capacitors thatmake up the EVCs join the circuit and charge. This part of the matchtune process takes about 55 μsec. Finally, the RF power profile 403 isshown decreasing, at just before t=56 μsec, from about 380 mVpeak-to-peak to about 100 mV peak-to-peak. This decrease in the RF powerprofile 403 represents the decrease in the reflected power 407, and ittakes place over a time period of about 10 μsec, at which point thematch tune process is considered complete.

The altering of the series variable capacitance and the shunt variablecapacitance can comprise sending a control signal to the series drivercircuit 39 and the shunt driver circuit 43 to control the seriesvariable capacitance and the shunt variable capacitance, respectively,where the series driver circuit 39 is operatively coupled to the seriesEVC 31, and the shunt driver circuit 43 is operatively coupled to theshunt EVC 43. When the EVCs 31, 33 are switched to their desiredcapacitance values, the input impedance may match the fixed RF sourceimpedance (e.g., 50 Ohms), thus resulting in an impedance match. If, dueto fluctuations in the plasma impedance, a sufficient impedance matchdoes not result, the process of 500A may be repeated one or more timesto achieve an impedance match, or at least a substantial impedancematch.

Using an RF matching network 11, such as that shown in FIG. 2, the inputimpedance can be represented as follows:

$Z_{in} = \frac{\left( {Z_{P} + Z_{L} + Z_{series}} \right)Z_{shunt}}{Z_{P} + Z_{L} + Z_{series} + Z_{shunt}}$

where Z_(in) is the input impedance, Z_(P) is the plasma impedance,Z_(L) is the series inductor impedance, Z_(series) is the series EVCimpedance, and Z_(shunt) is the shunt EVC impedance. In the exemplifiedembodiment, the input impedance (Z_(in)) is determined using the RFinput sensor 21. The EVC impedances (Z_(series) and Z_(shunt)) are knownat any given time by the control circuitry, since the control circuitryis used to command the various discrete capacitors of each of the seriesand shunt EVCs to turn ON or OFF. Further, the series inductor impedance(Z_(L)) is a fixed value. Thus, the system can use these values to solvefor the plasma impedance (Z_(P)).

Based on this determined plasma impedance (Z_(P)) and the known desiredinput impedance (Z_(in)′) (which is typically 50 Ohms), and the knownseries inductor impedance (Z_(L)), the system can determine a new seriesEVC impedance (Z_(series)′) and shunt EVC impedance (Z_(shunt)′).

$Z_{in}^{\prime} = \frac{\left( {Z_{P} + Z_{L} + Z_{series}^{\prime}} \right)Z_{shunt}^{\prime}}{Z_{P} + Z_{L} + Z_{series}^{\prime} + Z_{shunt}^{\prime}}$

Based on the newly calculated series EVC variable impedance(Z′_(series)) and shunt EVC variable impedance (Z′_(shunt)), the systemcan then determine the new capacitance value (first capacitance value)for the series variable capacitance and a new capacitance value (secondcapacitance value) for the shunt variable capacitance. When these newcapacitance values are used with the series EVC 31 and the shunt EVC 33,respectively, an impedance match may be accomplished.

The exemplified method of computing the desired first and secondcapacitance values and reaching those values in one step issignificantly faster than moving the two EVCs step-by-step to bringeither the error signals to zero, or to bring the reflectedpower/reflection coefficient to a minimum. In semiconductor plasmaprocessing, where a faster tuning scheme is desired, this approachprovides a significant improvement in matching network tune speed.

Determining Capacitance Values Using Parameter Matrix

FIG. 7 provides an alternative process 500 for matching an impedancethat uses a parameter matrix. In the exemplified process, the controlcircuit 45 (see FIG. 2 for matching network components) is configuredand/or programmed to carry out each of the steps. As one of two initialsteps, RF parameters are measured at the RF input 13 by the RF inputsensor 21, and the input impedance at the RF input 13 is calculated(step 501) using the measured RF parameters. For this exemplifiedprocess 500, the forward voltage and the forward current are measured atthe RF input 13. In certain other embodiments, the RF parameters may bemeasured at the RF output 17 by the RF output sensor 49, although insuch embodiments, different calculations may be required than thosedescribed below. In still other embodiments, RF parameters may bemeasured at both the RF input 13 and the RF output 17.

The impedance matching circuit, coupled between the RF source 15 and theplasma chamber 19, may be characterized by one of several types ofparameter matrices known to those of skill in the art, includingtwo-port parameter matrices. An S-parameter matrix and a Z-parametermatrix are two examples of such parameter matrices. Other examplesinclude, but are not limited to, a Y-parameter matrix, a G-parametermatrix, an H-parameter matrix, a T-parameter matrix, and anABCD-parameter matrix. Those of skill in the art will recognize alsothat these various parameter matrices may be mathematically convertedfrom one to the other for an electrical circuit such as a matchingnetwork. The second initial step of the exemplified process 500 is tolook up (step 502) the parameter matrix for the existing configurationof the impedance matching circuit in a parameter lookup table. Theexisting configuration of the impedance matching circuit is defined byexisting operational parameters of the impedance matching circuit,particularly the existing array configurations for both of the seriesEVC 31 and the shunt EVC 33. In order to achieve an impedance match, theexisting configuration of the impedance matching circuit is altered to anew configuration of the impedance matching circuit as part of theexemplified process 500.

The parameter lookup table includes a plurality of parameter matrices,with each parameter matrix being associated with a particularconfiguration of the series EVC 31 and the shunt EVC 33. The parameterlookup table may include one or more of the aforementioned types ofparameter matrices. In the exemplified process 500, the parameter lookuptable includes at least a plurality of S-parameter matrices. In certainembodiments, the parameter lookup table may include at least a pluralityof Z-parameter matrices. In embodiments in which the parameter lookuptable includes multiple types of parameter matrices, the different typesof parameter matrices are associated within the parameter lookup tablein such a way so as to eliminate the need for mathematical conversionsbetween the different types of parameter matrices. For example, theT-parameter matrix may be included as part of the parameter lookuptable, with each T-parameter matrix associated with the associatedS-parameter matrix that would result from conversion between the twomatrices.

The input impedance calculation (step 501) and the parameter matrix lookup (step 502) may be performed in any order. With the input impedancecalculated (step 501) and the parameter matrix for the existingconfiguration of the impedance matching circuit identified within theparameter lookup table (step 502) done, the plasma or load impedance maythen be calculated (step 503) using the calculated input impedance andthe parameter matrix for the existing configuration. Next, from thecalculated plasma impedance, the match configurations for the series EVC31 and the shunt EVC 33 that would achieve an impedance match, or atleast a substantial impedance match, between the RF source 15 and theplasma chamber 19 are looked up (step 504) in an array configurationlookup table. These match configurations from the array configurationlookup table are the array configurations which will result in newcapacitance values for the series EVC 31 and shunt EVC 33, with animpedance match being achieved with the new array configurations andassociated new capacitance values. The array configuration lookup tableis a table of array configurations for the series EVC 31 and the shuntEVC 33, and it includes each possible array configuration of the seriesEVC 31 and the shunt EVC 33 when used in combination. As an alternativeto using an array configuration lookup table, the actual capacitancevalues for the EVCs 31, 33 may be calculated during the process—however,such real-time calculations of the capacitance values are inherentlyslower than looking up the match configurations in the arrayconfiguration lookup table. After the match configurations for theseries EVC 31 and the shunt EVC 33 are identified in the arrayconfiguration lookup table, then one or both of the series arrayconfiguration and the shunt array configuration are altered (step 505)to the respective identified match configurations for the series EVC 31and the shunt EVC 33.

The altering (step 505) of the series array configuration and the shuntarray configuration may include the control circuit 45 sending a controlsignal to the series driver circuit 39 and the shunt driver circuit 43to control the series array configuration and the shunt arrayconfiguration, respectively, where the series driver circuit 39 isoperatively coupled to the series EVC 31, and the shunt driver circuit43 is operatively coupled to the shunt EVC 43. When the EVCs 31, 33 areswitched to the match configurations, the input impedance may match thefixed RF source impedance (e.g., 50 Ohms), thus resulting in animpedance match. If, due to fluctuations in the plasma impedance, asufficient impedance match does not result, the process of 500 may berepeated one or more times to achieve an impedance match, or at least asubstantial impedance match.

The lookup tables used in the process described above are compiled inadvance of the RF matching network being used in conjunction with theplasma chamber 19. In creating the lookup tables, the RF matchingnetwork 11 is tested to determine at least one parameter matrix of eachtype and the load impedance associated with each array configuration ofthe series EVC 31 and the shunt EVC 33 prior to use with a plasmachamber. The parameter matrices resulting from the testing are compiledinto the parameter lookup table so that at least one parameter matrix ofeach type is associated with a respective array configuration of theEVCs 31, 33. Similarly, the load impedances are compiled into the arrayconfiguration lookup table so that each parameter matrix is associatedwith a respective array configuration of the EVCs 31, 33. Thepre-compiled lookup tables may take into consideration the fixed RFsource impedance (e.g., 50 Ohms), the power output of the RF source, andthe operational frequency of the RF source, among other factors that arerelevant to the operation of the RF matching network. Each lookup tablemay therefore have tens of thousands of entries, or more, to account forall the possible configurations of the EVCs 31, 33. The number ofpossible configurations is primarily determined by how many discretecapacitors make up each of the EVCs 31, 33. In compiling the lookuptables, consideration may be given to possible safety limitations, suchas maximum allowed voltages and currents at critical locations insidethe matching network, and this may serve to exclude entries in one ormore of the lookup tables for certain configurations of the EVCs 31, 33.

As is known in the art, the S-parameter matrix is composed of componentscalled scatter parameters, or S-parameters for short. An S-parametermatrix for the impedance matching circuit has four S-parameters, namelyS₁₁, S₁₂, S₂₁, and S₂₂, each of which represents a ratio of voltages atthe RF input 13 and the RF output 17. All four of the S-parameters forthe impedance matching circuit are determined and/or calculated inadvance, so that the full S-parameter matrix is known. The parameters ofthe other types of parameter matrices may be similarly determined and/orcalculated in advance and incorporated into the parameter matrix. Forexample, a Z-parameter matrix for the impedance matching circuit hasfour Z-parameters, namely Z₁₁, Z₁₂, Z₂₁, and Z₂₂.

By compiling the parameter lookup table in this manner, the entire timecost of certain calculations occurs during the testing phase for the RFmatching network, and not during actual use of the RF matching network11 with a plasma chamber 19. Moreover, because locating a value in alookup table can take less time than calculating that same value in realtime, using the lookup table can aid in reducing the overall time neededto achieve an impedance match. In a plasma deposition or etching processwhich includes potentially hundreds or thousands of impedance matchingadjustments throughout the process, this time savings can help adddirectly to cost savings for the overall fabrication process.

From the beginning of the match tune process, which starts with thecontrol circuit determining the variable impedance of the plasma chamberand determining the series and shunt match configurations, to the end ofthe match tune process, when the RF power reflected back toward the RFsource decreases, the entire match tune process of the RF impedancematching network using EVCs has an elapsed time of approximately 110μsec, or on the order of about 150 μsec or less. This short elapsed timeperiod for a single iteration of the match tune process represents asignificant increase over a VVC matching network. Moreover, because ofthis short elapsed time period for a single iteration of the match tuneprocess, the RF impedance matching network using EVCs may iterativelyperform the match tune process, repeating the two determining steps andthe generating another control signal for further alterations to thearray configurations of one or both of the electronically variablecapacitors. By iteratively repeating the match tune process, it isanticipated that a better impedance match may be created within about2-4 iterations of the match tune process. Moreover, depending upon thetime it takes for each repetition of the match tune process, it isanticipated that 3-4 iterations may be performed in 500 μsec or less.Given the 1-2 sec match time for a single iteration of a match tuneprocess for RF impedance matching networks using VVCs, this ability toperform multiple iterations in a fraction of the time represents asignificant advantage for RF impedance matching networks using EVCs.

Those of skill in the art will recognize that several factors maycontribute to the sub-millisecond elapsed time of the impedance matchingprocess for an RF impedance matching network using EVCs. Such factorsmay include the power of the RF signal, the configuration and design ofthe EVCs, the type of matching network being used, and the type andconfiguration of the driver circuit being used. Other factors not listedmay also contribute to the overall elapsed time of the impedancematching process. Thus, it is expected that the entire match tuneprocess for an RF impedance matching network having EVCs should take nomore than about 500 μsec to complete from the beginning of the process(i.e., measuring by the control circuit and calculating adjustmentsneeded to create the impedance match) to the end of the process (thepoint in time when the efficiency of RF power coupled into the plasmachamber is increased due to an impedance match and a reduction of thereflected power). Even at a match tune process on the order of 500 μsec,this process time still represents a significant improvement over RFimpedance matching networks using VVCs.

Table 1 presents data showing a comparison between operationalparameters of one example of an EVC versus one example of a VVC. As canbe seen, EVCs present several advantages, in addition to enabling fastswitching for an RF impedance matching network:

TABLE 1 Typical 1000 pF Parameter EVC Vacuum Capacitors Capacitance 20pF~1400 pF  15 pF~1000 pF Reliability High Low Response Time ~500 μsec 1s~2 s ESR ~13 mW ~20 mW Voltage 7 kV 5 kV Current Handling Capability216 A rms 80 A rms Volume 4.5 in³ 75 in³

As is seen, in addition to the fast switching capabilities made possibleby the EVC, EVCs also introduce a reliability advantage, a currenthandling advantage, and a size advantage. Additional advantages of theRF impedance matching network using EVCs and/or the switching circuititself for the EVCs include:

-   -   The disclosed RF impedance matching network does not include any        moving parts, so the likelihood of a mechanical failure reduced        to that of other entirely electrical circuits which may be used        as part of the semiconductor fabrication process. For example,        the typical EVC may be formed from a rugged ceramic substrate        with copper metallization to form the discrete capacitors. The        elimination of moving parts also increases the resistance to        breakdown due to thermal fluctuations during use.    -   The EVC has a compact size as compared to a VVC, so that the        reduced weight and volume may save valuable space within a        fabrication facility.    -   The design of the EVC introduces an increased ability to        customize the RF matching network for specific design needs of a        particular application. EVCs may be configured with custom        capacitance ranges, one example of which is a non-linear        capacitance range. Such custom capacitance ranges can provide        better impedance matching for a wider range of processes. As        another example, a custom capacitance range may provide more        resolution in certain areas of impedance matching. A custom        capacitance range may also enable generation of higher ignition        voltages for easier plasma strikes.    -   The short match tune process (˜500 μsec or less) allows the RF        impedance matching network to better keep up with plasma changes        within the fabrication process, thereby increasing plasma        stability and resulting in more controlled power to the        fabrication process.    -   The use of EVCs, which are digitally controlled, non-mechanical        devices, in an RF impedance matching network provides greater        opportunity to fine tune control algorithms through programming.    -   EVCs exhibit superior low frequency (kHz) performance as        compared to VVCs.

Altering Frequency of RF Source to Fine Tune Match

FIG. 8 is a flow chart showing a process 600 for matching an impedanceaccording to another embodiment. Since EVCs can provide only discretizedcapacitance values, a matching network that varies only EVCs to createan impedance match can only match based on these discretized values. Forexample, if a plasma impedance occurs such that the series and/or shuntcapacitance values needed to bring the input impedance of the matchingnetwork to a desired non-reactive 50 Ohms lies in-between thediscretized values, the EVC-based matching network will not be able totune the input impedance of the matching network to the non-reactive 50Ohms. The process 600 of FIG. 8 addresses such a circumstance by alsoaltering a frequency of the RF source (sometimes referred to as the “RFgenerator”) to carry out the impedance match.

The RF source, matching network, and plasma chamber of process 600 canbe configured similarly to the system of FIG. 2. Accordingly, referencewill be made to the components of the system of FIG. 2, though thisfigure represents just one embodiment of the invention.

As with previously discussed embodiments, the matching network 11 ofprocess 600 can include an RF input 13 configured to receive an RFsignal from an RF source 15, and an RF output 17 configured to operablycouple to a plasma chamber 19. The matching network can further includeat least one EVC 31, 33, and a control circuit 45 for instructing the atleast one EVC 31, 33 to alter its variable capacitance. The RF source 15(including its control circuitry) and the RF matching network 11 can bein the same enclosure or separate enclosures.

In the process 600, the matching network 11 is initially in an autotuning mode (step 601). In this mode, the matching network 11 can beconfigured to carry out automated tuning by altering at least onecapacitance value in a manner similar to that described in the foregoingembodiments. In this mode, the process 600 performs tuning referred toas primary tuning (step 602). In the exemplified embodiment, the primarytuning includes altering the series and/or shunt capacitance values inan attempt to achieve an impedance match. In the exemplified embodiment,the desired input impedance (the desired impedance at the input of thematching network 11) is a fixed, non-reactive 50 Ohm, sometimes referredto as the RF source impedance. In other embodiments, the desired inputimpedance can be any other impedance value, and can be variable.

In the exemplified embodiment, the primary tuning will bring the inputimpedance relatively close to a non-reactive 50 Ohms, the matchingnetwork 11 being limited by the discretized capacitance values of theEVCs 31, 33. At this stage, a preliminary match is achieved (step 603).The preliminary match state will have an associated first reflectionparameter value at the RF source output 15 a (the RF source output 15 abeing connected to the matching network input 13). In the exemplifiedembodiment, the first reflection parameter value is a reflected powervalue. In other embodiments, the first reflection parameter value can beany reflection-related parameter associated with the preliminary matchstate. For example, the first reflection parameter value can be thereflection coefficient, which represents the ratio of the amplitude ofthe reflected wave to the incident wave, and is sometimes referred to asgamma. The first reflection parameter can be measured by sensor 21 atthe RF source output 15 a. In other embodiments, reflected power can bemeasured by a sensor or comparable device that is located proximate tothe matching network input 13.

In one embodiment, the alteration of variable capacitance in auto tuningmode can include the steps of adjusting the variable capacitance,determining an intermediate reflection parameter value, and thenreducing and/or increasing the variable capacitance based on theintermediate reflection parameter value. This process can be repeatedsuch that there are several intermediate reflection parameter values,the adjustment of the one or more variable capacitances being based onthese intermediate reflection parameter values. In other embodiments,the invention can omit the use of intermediate reflection parametervalues.

Once the preliminary match state is achieved, the matching network 11can provide a control signal to the RF source 15 indicating that primarytuning is complete and that a preliminary match has been achieved (step604). The control signal can be any signal sufficient to provideindication that the preliminary match has been achieved.

In response, the RF source 15 can send a hold signal to the matchingnetwork 11 (step 605), the hold signal placing the matching network 11in a manual tuning mode (step 606). In manual tuning mode, the matchingnetwork 11 will stop performing automated tuning (and therefore will notalter the variable capacitances) as long as the hold signal is present.In other embodiments, the matching network 11 can automatically entermanual tuning mode when the preliminary match has been achieved, and canreturn to auto tuning mode when receiving an instruction from the RFsource 15.

Next, the variable frequency of the RF source 15 can be adjusted toperform secondary tuning (step 607). This secondary tuning can fine tunethe input impedance of the matching network 1 to the desirednon-reactive 50 Ohm, or other desired impedance, and can minimize thereflected power at the output of the RF source 15, thereby alsodecreasing the reflection coefficient. The RF source 15 can havestandard control circuitry by which the frequency is varied and thesignals discussed above are sent, received, and processed. The frequencycan be altered by providing a command to a frequency generation circuitthat forms part of the RF source, such as a Direct Digital Synthesizer.

Once the RF source 15 has completed altering the frequency for thesecondary tuning, a final match state is achieved (step 608). The finalmatch state will have an associated second reflection parameter value atthe RF source output 15 a. As with the first reflection parameter value,in the exemplified embodiment, the second reflection parameter value isa reflected power value. In other embodiments, the second reflectionparameter value can be any reflection-related parameter associated withthe preliminary match state, such as the reflection coefficient(discussed above). The second reflection parameter can be measured by asensor 21 at the RF source output 15 a. Since the final match statecauses a more finely tuned match than the preliminary match state, thesecond reflection parameter value will be less than the first reflectionparameter value.

The alteration of the variable RF source frequency can include reducingand/or increasing the variable RF source frequency based on anintermediate reflection parameter value. In one embodiment, thealteration of the variable source frequency includes reducing thevariable RF source frequency by a first amount and determining theintermediate reflection parameter value at the RF source output. If theintermediate reflection parameter value decreases, the variable RFsource frequency is again reduced by the first amount and a newintermediate reflection parameter value is measured. This process canrepeat until the intermediate reflection parameter value increases. Whenthe intermediate reflection parameter value increases, the variablesource frequency can be increased by a second amount (the second amountbeing less than the first amount), and then a new intermediatereflection parameter value is determined. If the new intermediatereflection parameter value decreases, the variable source frequency isagain increased by the second amount, and a new intermediate reflectionparameter value is determined. This process can repeat until the newintermediate reflection parameter value increases or is zero, at whichstage the process can stop or the variable source frequency can bereturned to its previous value.

The invention is not limited to any one embodiment for tuning thefrequency or variable capacitance. For example, the invention can useany variety of methods to step up and/or down the frequency in differentincrements based on the resulting reflected power. Further, the process600 can have a minimum reflected parameter value (e.g., a minimumreflected power or minimum reflection coefficient). When the minimumreflected parameter value is achieved, the tuning can stop, regardlessof whether the process is in primary or secondary tuning.

Returning to the exemplified embodiment, once the final match state isachieved, the RF source 15 can send a signal (sometimes referred to as a“resume signal”) to the matching network 11 to place the matchingnetwork 11 back into auto tuning mode (step 609). The matching network11 can then be ready for the next variation of the plasma impedance.Thus, when a plasma impedance of the plasma chamber 15 changes, thecontrol circuit 45 can repeat the instruction to alter the variablecapacitance and/or the instruction to alter the variable RF sourcefrequency.

In other embodiments, the process 600 will not resume tuning until thereflection parameter value exceeds a predetermined value. Such a tuningrestart threshold can be applied to the primary tuning, the secondarytuning, or both. Further, thresholds can be set such that, for smallreflected power level raises, only secondary tuning is done (alteringthe RF source frequency), while, for larger reflected power levels,primary tuning is first carried out (altering capacitances), followed bysecondary tuning (altering the RF source frequency).

Combining an EVC-based RF matching network with a variable frequency RFsource provides several advantages for fast and precise RF matching. Forexample, with all components being electronic, the system has higherreliability than those using VVC technology, which are prone tomechanical failures. Further, the primary and second tuning can beperformed quickly to enable matching within 500 μsec. Further, thecombined EVC matching network and variable RF source can decrease thereflected power to the RF source to essentially 0 Watts.

Restricted Capacitor Switching

The matching networks discussed above can alter their variablecapacitance values to achieve an impedance match. This process issometimes referred to as tuning. The state of the impedance matching canbe assessed based on a reflection parameter value. In the exemplifiedembodiments, the reflection parameter value is a reflected power value.More specifically, the reflection parameter value is a reflectioncoefficient value (sometimes referred to as “gamma”), which representsthe ratio of the amplitude of a reflected wave to an incident wave.Referring to the system 85 of FIG. 2, the reflection parameter value canbe measured by sensor 21 at the matching network input 13 (or RF source15 output), or by sensor 49 at the matching network output 17 (or plasmachamber 19 input). Such a sensor can provide a signal to the controlcircuit 45 indicative of the reflection parameter value. In otherembodiments, the reflection parameter value can be anyreflection-related parameter associated with a match state.

In one approach to achieving an impedance match, a matching algorithmrequires the control loop of the RF matching network to continue to tuneuntil the reflection coefficient value at the input of the matchingnetwork is reduced below a certain level. This level is sometimesreferred to as “gamma-stop.” If the load impedance changes, thereflection coefficient at the input of the RF matching network canincrease. If this reflection coefficient increases beyond a certainreflection coefficient value, sometimes referred to as “gamma-restart,”then the RF matching network starts to tune again. In a solid-state RFmatching network, there are typically no restrictions on how manyswitches can switch ON or OFF at any time, therefore based on the changein the reflection coefficient, the number of switches switching at anytime can be significant and thus can result in perturbing the plasma tomake it unstable.

In an alternative approach, an intermediate gamma value is utilized suchthat there are three gamma values: (1) a first reflection value(gamma-stop) at which tuning is stopped, (2) a second reflection value(gamma-restart-low) at which capacitor switching is limited, and (3) athird reflection value (gamma-restart-high) at which capacitor switchingis unlimited.

FIG. 9 is flow chart showing a process for matching an impedance wherecapacitor switching can be restricted using the above reflection values.In the exemplified embodiment, the reflection coefficient value iscontinuously monitored (operation 202). When the match is tuned and thereflection coefficient value (gamma) is not above the first reflectionvalue (operation 204), no capacitors switch (operation 210). When thereflection coefficient value goes above the second reflection value (butis at or below the third reflection value) (operation 206), only apredetermined number of predetermined fine capacitors can switch at thistime (restricted tune) (operation 212). Whether to turn these switchesON or OFF will depend upon what was the actual calculated position ofthe capacitors. When the reflection coefficient value goes above thethird reflection value (operation 208), the capacitors can switchwithout any restrictions (unrestricted tune) (operation 214). For thepurpose of this description, the fine capacitors can be any capacitorsthat are used to provide finer capacitance movement steps than thecoarse capacitors. In one embodiment, the coarse capacitors have acapacitance at least twice as large as the capacitance of the finecapacitors.

In one example, the predetermined number is two (only two capacitors canswitch when the reflection coefficient value initially exceeds thesecond reflection value), and the three reflection values are asfollows: (1) first reflection value (gamma-stop)=0.031, (2) secondreflection value (gamma-restart-low)=0.07, (3) third reflection value(gamma-restart-high)=0.10. In this example, the matched position isC4F5/C6F7 (i.e., 4 coarse capacitor switches ON and 5 fine capacitorswitches ON for one solid state capacitor array, and 6 coarse capacitorswitches ON and 7 fine capacitor switches ON for the second solid statecapacitor array), and this positioning is determined before determininghow to switch the discrete capacitors.

If the reflection coefficient value is calculated as 0.08, and the newtuned position is calculated to be C3F0/C7F1, then the match will go toC4F3/C6F9, rather than going directly to C3F0/C7F1. The control circuitcan continuously monitor the reflection coefficient value (or otherreflection parameter), and thus this loop can run as many times asneeded until either the reflection coefficient value goes below thefirst reflection value or the reflection coefficient value goes abovethe third reflection value. If the reflection coefficient value goesabove the third reflection value (i.e., 0.10), then the capacitorswitches are not restricted and can directly switch to the calculatedposition. Note that the foregoing capacitor restrictions can also beapplied to when the match is moving from a higher reflection coefficientvalue to a lower reflection coefficient value to provide a slowersettling profile. Not also, while the embodiment described abovediscusses altering the tuning based on whether a reflection parameter isabove, or at, or below a reflection parameter (or some combinationthereof), other embodiments can use any one of these options (or acombination of options) provided different values are used as referencevalues for determining what type of tuning to use. For example, in oneembodiment the system can carry out an unrestricted tune when thereflection parameter is above the third reflection value, while inanother embodiment the system can carry out an unrestricted tune whenthe reflection parameter is at or above the third reflection value.

By the above multi-step reflection value approach, if something changesin the process that changes the impedance by a significant amount, thenthe match can respond faster, but if the change is small, then the matchwill not take big steps to cause the plasma to become unstable. Thisrestricted capacitor switching approach can be used, for example, withthe matching networks discussed above. A control circuit, such ascontrol circuit 45 or 645 can be used to carry out the steps ofdetermining or receiving the reflection parameter value and controllingthe altering of the discrete capacitors based on that value. It isfurther noted that the restricted capacitor approach described above canbe used in conjunction with the other impedance matching andcapacitor-switching methods discussed herein. Further, the restrictedcapacitor switching approach can be used with a matching network thatforms part of a semiconductor processing tool, such as that shown inFIGS. 1-3. Further, the restricted capacitor switching approach can beused with a matching network as part of a method of manufacturing asemiconductor.

Matching Using EVC and Frequency

In yet another embodiment, impedance matching can be carried out usingan EVC and frequency considerations. According to one embodiment, asingle EVC is used. For example, in FIG. 3, capacitor 33A can be an EVC,while capacitor 31A can be non-variable. (In other embodiments, morethan one capacitor in the matching network can be variable.) Thematching network can be calibrated such that post-calibration, at leastone of the lookup tables (such as the lookup tables discussed above)contains information to provide the best combination of capacitorposition and frequency for a load impedance to get the lowest inputreflected power or input reflection coefficient (input gamma).

During operation, in one embodiment the matching network determines theinput impedance based on the information provided by an input RF sensor,such as a VI (voltage-current) sensor located at the RF input of thematching network. The matching network then uses this input impedanceinformation and the current EVC configuration (e.g., capacitor switchpositions) and the frequency information to calculate the plasma chamber(load) impedance. Alternatively, rather than calculating the loadimpedance from input impedance and the calibration parameters of thematch, the load impedance can be directly measured from an output sensorat the RF output of the matching network.

In the next step of this embodiment, the matching network uses thedetermined load impedance and the match lookup table to determine thenew EVC configuration and the new frequency that would provide thelowest reflected power or lowest input reflection coefficient at the RFinput for enabling an impedance match. Such an approach provides a muchfaster means for tuning compared to linearly changing the capacitorswitch positions and frequency based on the polarity and magnitude ofthe input error signal.

When the matching network is coupled to a plasma chamber and operating,the RF source (e.g., an RF generator) or the customer's system canprovide the matching network with the frequency signal through somecommunication port (e.g., analog). Alternately, the matching network candetect the frequency at its RF input port. Based on this specificfrequency, the matching network can use the lookup table to determinewhat EVC configuration, for that frequency, provides the lowest inputreflected power or input reflection coefficient (gamma) for enabling animpedance match. The matching network's control circuit can then choosethis EVC position and command the discrete switches of the EVC to switchthe EVC to this new configuration providing a new capacitance.

In another embodiment, the matching network can determine the best EVCconfiguration and frequency combination to provide the lowest inputreflected power or input reflection coefficient (gamma). The matchingnetwork's control circuit can then move the EVC to the new configuration(e.g., desired switch positions) and at the same time command the RFgenerator to move to the desired frequency. For example, this method canuse EVC technology for the EVC and frequency tuning for the other legand make an ‘L’ or ‘pi’ type of match for higher power operation, up to6 or 10 kW.

Returning to FIG. 3, this semiconductor processing system 85A can beunderstood as carrying out one or more of the embodiments discussedabove. The matching network 11A has an input 13 coupled to an RF source15 having a variable frequency, and an output coupled to a plasmachamber 19 having a variable chamber impedance. The matching network 11Afurther includes two capacitors, where capacitor 33A may be an EVC andcapacitor 31A may be non-variable. The matching network 11A has acontrol circuit 45 coupled to at least one of sensors 21 and sensor 49,the one or more sensors configured to detect an RF parameter. Thecontrol circuit may use a match lookup table (such as one of the lookuptables discussed above) with a value based on the detected RF parameterto determine a match combination. The match combination includes both anew EVC configuration for providing a new EVC capacitance, and a newsource frequency for the RF source. Once these determinations have beenmade, the control circuit 45 can alter the EVC 33A to the new EVCconfiguration (and thus provide a new capacitance) and alter thevariable frequency of the RF source to the new source frequency.

In other embodiments, the match combination may instead be only a newEVC configuration, where the lookup table bases this configuration onthe current frequency being provided by the RF source. In such anembodiment, the RF source may be controlled by a separate second controlcircuit 16.

In the exemplified embodiment, the value based on the detected RFparameter (used with the match lookup table) is the variable chamberimpedance. In other embodiments, the RF parameter can be any RFparameter associated with the matching network or processing system. Forexample, the RF parameter may be detected at the RF input 13 (by sensor21) or at the RF output 17 (by sensor 49). In some embodiments, thevalue based on the detected RF parameter can be the detected RFparameter itself.

In the exemplified embodiment, the EVC comprises discrete capacitorshaving different configurations defining ON and OFF states of thediscrete capacitors, these different configurations causing the EVC toprovide different capacitances. For example, each discrete capacitor mayhave a corresponding switch to activate or deactivate the discretecapacitor, the EVC being altered to a new EVC configuration by theswitches activating or deactivating at least one of the discretecapacitors of the EVC. The corresponding switch may be in series with orparallel to the discrete capacitor.

In one embodiment, prior to an impedance match, the EVC has a firstconfiguration defining ON and OFF states of the discrete capacitors, andthe variable frequency of the RF source has a first frequency. Thecontrol circuit determines, based on the detected RF parameter, an inputimpedance at the RF input of the matching network. The control circuitthen determines the variable chamber impedance from a parameter matrixlookup table using (1) the determined input impedance of the impedancematching network; (2) the first configuration of the EVC; and (3) thefirst frequency of the RF source. The control circuit then uses thedetermined variable chamber impedance with the match lookup table todetermine the match combination. The sensor may be a voltage and currentsensor positioned at the RF input of the matching network. Further, theparameter matrix lookup table may include two-port parameter matrices,such as S-parameter matrices or Z-parameter matrices.

In another embodiment, the RF sensor 21 is a phase or magnitude detectoroperably coupled to the RF input 13 of the matching network 11A, and thedetected RF parameter used for the determination of the matchcombination is a phase error or a magnitude error. In anotherembodiment, the RF sensor is operably coupled to the RF input of thematching network, and the detected RF parameter is at least one of avoltage, a current, or a phase at the RF input. Further, thedetermination of the match combination may use the match lookup tablewith a reflection coefficient based on the at least one of the voltage,the current, or the phase, the reflection coefficient being the valuebased on the detected RF parameter. In yet another embodiment, the RFsensor 49 is operably coupled to the RF output 17 of the matchingnetwork, and the determination of the match combination uses the matchlookup table with a load impedance based on the RF parameter detected bythe RF sensor at the RF output.

FIG. 10 is a flow chart showing an embodiment of a process 110 formatching an impedance using a lookup table to alter an EVC configurationand an RF source frequency. In a first step, the sensor detects an RFparameter (step 112). To cause an impedance match between the RF sourceand the plasma chamber, the control circuit determines, using a matchlookup table with value based on the detected RF parameter, a matchcombination of a new EVC configuration for providing a new EVCcapacitance, and a new source frequency for the RF source (step 114).The control circuit then alters the EVC to the new EVC configuration,and alters the variable frequency of the RF source to the new sourcefrequency (step 116).

The above process may be carried out as part of a method ofmanufacturing a semiconductor. Such a manufacturing method may includeplacing a substrate in the plasma chamber configured to deposit amaterial layer onto the substrate or etch a material layer from thesubstrate; and energizing plasma within the plasma chamber by couplingRF power from the RF source into the plasma chamber to perform adeposition or etching. Further, the matching network described above mayform part of a semiconductor processing tool (such as tool 86 in FIG.3), the tool including the plasma chamber 19 and the matching network11A.

Matching Using Independent EVC and Frequency Control

In yet another embodiment, impedance matching can be carried out usingan EVC and frequency considerations where the EVC and the frequency arecontrolled separately. According to one embodiment, a single EVC isused. For example, in FIG. 3, capacitor 33A can be an EVC, whilecapacitor 31A can be non-variable. In other embodiments, more than onecapacitor in the matching network can be variable, or capacitor 31A canbe eliminated. The matching network can be calibrated such thatpost-calibration, at least one of the lookup tables (such as the lookuptables discussed above) contains information to provide the bestcapacitor positions for a load impedance to have the lowest inputreflected power or input reflection coefficient (input gamma).

During operation, the matching network can determine the input impedanceby those methods described above with respect to FIG. 10, such as byusing a VI (voltage-current) sensor located at the RF input of thematching network. Also similar to the embodiments discussed above, thematching network can use the input impedance information and the currentEVC configuration (e.g., capacitor switch positions) and the frequencyinformation to calculate a load impedance. Alternatively, rather thancalculating the load impedance from input impedance and the calibrationparameters of the match, the load impedance can be directly measuredfrom an output sensor at the RF output of the matching network. In theexemplified embodiment, the load impedance to be calculated or otherwisedetermined is the impedance at the EVC output (see, e.g., EVC output 41Bof FIG. 12). In certain embodiments, this load impedance is the variablechamber impedance and the impedance of the frequency-sensitive circuit(see frequency-sensitive circuit 37B of FIG. 12), though the inventionto a particular load impedance.

Similar to the embodiments related to FIG. 10, the matching network canuse the determined load impedance and the match lookup table todetermine a new EVC configuration to provide a lower reflected power orinput reflection coefficient at the RF input for helping enable animpedance match. Unlike the embodiment of FIG. 10, however, the newfrequency provided by the RF source is determined independently of thedetermination of the new EVC configuration.

Returning to FIG. 3, the semiconductor processing system 85A can beunderstood as carrying out one or more of the embodiments discussedabove. The matching network 11A has an input 13 coupled to an RF source15 having a variable frequency, and an output coupled to a plasmachamber 19 having a variable chamber impedance. The matching network 11Afurther includes two capacitors, where capacitor 33A may be an EVC andcapacitor 31A may be non-variable. The matching network 11A has a firstcontrol circuit 45 coupled to at least one of sensors 21 and sensor 49,the one or more sensors configured to detect an RF parameter. Thecontrol first circuit 45 may use a match lookup table (such as one ofthe lookup tables discussed above) with a value based on the detected RFparameter to determine a new EVC configuration for providing a new EVCcapacitance. Once these determinations have been made, the first controlcircuit 45 can alter the EVC 33A to the new EVC configuration andthereby assist in causing an impedance match between the RF source andthe plasma chamber. In one embodiment, this altering of the EVCconfiguration can be understood as one step towards causing an impedancematch (the change in frequency being a different and separate step). Inthese embodiments, the first control circuit 45 controlling the EVC isseparate and distinct from a second control circuit 16 for controllingthe frequency of the RF source.

In the exemplified embodiment, the second control circuit 16 alters thevariable frequency of the RF source 15, independently from the firstcontrol circuit, to further cause the impedance match between the RFsource and the plasma chamber. In one embodiment, this frequencyaltering can be understood as a second (and possibly final) step incausing an impedance match, though the time of occurrence of the twosteps may to some extent overlap. The first control circuit 45 does notprovide instructions to the second control circuit 16 for controllingthe variable frequency of the RF source 15. The second control circuit'sfrequency alteration occurs independently from the first controlcircuit.

In certain embodiments, the second control circuit can form part of theRF source. In other embodiments, the second control circuit can formpart of the matching network. In yet other embodiments, the secondcontrol circuit can be distinct from both the RF source and the matchingnetwork.

In the exemplified embodiment, the value based on the detected RFparameter (used with the match lookup table) is the load impedance(e.g., the impedance at the EVC 33A output). In other embodiments, theRF parameter can be any RF parameter associated with the matchingnetwork or processing system. For example, the RF parameter may bedetected at the RF input 13 (by sensor 21) or at the RF output 17 (bysensor 49). In some embodiments, the value based on the detected RFparameter can be the detected RF parameter itself. As with earlierembodiments, the EVC comprises discrete capacitors having differentconfigurations defining ON and OFF states of the discrete capacitors,these different configurations causing the EVC to provide differentcapacitances.

In one embodiment, prior to an impedance match, the EVC has a firstconfiguration defining ON and OFF states of the discrete capacitors. Thefirst control circuit determines, based on the detected RF parameter, aninput impedance at the RF input of the matching network. The controlcircuit then determines the load impedance from a parameter matrixlookup table using (1) the determined input impedance of the impedancematching network; and (2) the first configuration of the EVC. Thecontrol circuit then uses the determined load impedance with the matchlookup table to determine the new EVC configuration. The sensor may be avoltage and current sensor positioned at the RF input of the matchingnetwork. Further, the parameter matrix lookup table may include two-portparameter matrices, such as S-parameter matrices or Z-parametermatrices. Further, the RF sensor may have any of the characteristicdiscussed above with regard to the previous embodiments, and thedetermination of the EVC configuration may use the match lookup tablewith a reflection coefficient.

FIG. 11 is a flow chart showing an embodiment of a process 120 formatching an impedance where capacitance and frequency are adjustedindependently. The process 120 includes an EVC subprocess 121 and afrequency subprocess 125 operating in parallel and independently. Forthe EVC subprocess 121, in a first step the sensor detects an RFparameter (step 122). To assist in causing an impedance match betweenthe RF source and the plasma chamber, the first control circuitdetermines, using a match lookup table with value based on the detectedRF parameter, a new EVC configuration for providing a new EVCcapacitance (step 123). The first control circuit then alters the EVC tothe new EVC configuration (step 124).

For the frequency subprocess 125, in a first step the second controlcircuit determines an RF parameter. In one embodiment, the RF parameteris a reflected power or reflection coefficient at the RF source output,though the invention is not so limited. In a second step, the secondcontrol circuit alters an RF source frequency based on the determined RFparameter.

The above process may be carried out as part of a method ofmanufacturing a semiconductor. Such a manufacturing method may includeplacing a substrate in the plasma chamber configured to deposit amaterial layer onto the substrate or etch a material layer from thesubstrate; and energizing plasma within the plasma chamber by couplingRF power from the RF source into the plasma chamber to perform adeposition or etching. Further, the matching network described above mayform part of a semiconductor processing tool (such as tool 86 in FIG.3), the tool including the plasma chamber 19 and the matching network11A.

FIG. 12 is a schematic of an embodiment of a matching network 11B havinga frequency-sensitive circuit 37B responsive to frequency adjustments.The frequency-sensitive circuit is designed to have an impedance thatcan vary significantly when the variable frequency of the RF source isaltered. In the exemplified embodiment, the frequency-sensitive circuit37B includes an LC circuit 38B having a capacitor 34B and an inductor35B. The frequency-sensitive circuit 37B can further include seriescapacitor 36B. In one embodiment, the variable chamber impedance canprovide an inductance or capacitance for the LC circuit. The matchingnetwork 11B includes an input 13B and an output 17B. It further includesan EVC 33B having an EVC output 41B. A second capacitor 39B can also beincluded. This capacitor can be, for example, an EVC, a variablecapacitor that is not an EVC (e.g., a vacuum variable capacitor), or anon-variable capacitor. As discussed, the determination of the new EVCconfiguration can use a match lookup table with a load impedance, andthe load impedance in certain embodiments can be an impedance at anoutput 41B of the EVC, the EVC output impedance being the value based onthe detected RF parameter. Further, the EVC output impedance can be thevariable chamber impedance and the impedance of the frequency-sensitivecircuit forming part of the impedance matching network.

The exemplified embodiment of FIG. 11 addresses the issue that thematching network may not be able control the frequency of the RF source.Further, communications between the match and generator may be slow, sothey may not be able to send the frequency information fast enough forfast tuning. The current invention is based on the discovery that thematching network can match without knowledge of the frequency, or anyfrequency tuning being carried out by the generator. The matchingnetwork can view the frequency tuning elements as part of the load.Simulations were run to confirm the results, as well as testing units onstatic loads.

Simulations

Two tests were run, one on a 400 kHz variable matching network and theother on a 13.56 MHz variable matching network. The matching circuitswere altered by adding capacitors around the inductor in both paralleland in series, as can be seen in FIG. 12. The frequency range for the400 kHz unit is 360 kHz to 440 kHz, ±10%, and the shunt capacitor variesfrom 200 pF to 38,960 pF. For the 13.56 MHz unit, the frequency range is12.88 MHz to 14.24 MHz, ±5%, and the capacitor range of 290 pF to 1910pF. These are simplified models, as not all ESRs and other parasiticsare accounted for.

As the frequency sweeps, the parallel capacitor gives the inductor ahigher impedance at one end of the spectrum, while the series capacitorgives a lower inductance at the other end of the spectrum. In the caseof the 13.56 MHz match, the circuit resonates and has a capacitiveimpedance at one end of the spectrum. This is what gives the frequencytuning its impedance variability on the imaginary axis.

The two matching circuits were then tested to verify that they were ableto match fixed loads, and as a reference for later testing. This wasdone manually by varying the capacitor, and then the frequency. Thesetwo steps were then repeated until the VSWR was below an acceptablelevel, which was 1.1:1. The 400 kHz matched a load impedance of 45-j372,with a capacitance of approximately 12,197 and frequency of 416.9 kHzwith a VSWR of 1.03:1. The 13.56 MHz unit also tuned into a fixed loadwith a frequency of 13.99 MHz and capacitance of about 425 pF.

The next set of testing assumed that the matching network neither hascontrol of the generator, or any knowledge of the frequency. There aremultiple reasons why this could be the case, as stated above. The firststep was to remove the frequency-sensitive portion of the match. Thisleaves only the variable capacitor. This was done using a circuitsimilar to matching network 11B of FIG. 12, but wherefrequency-sensitive portion 37B and capacitor 39B are eliminated. Thenext step was to simulate and measure the two-port network parameters.FIG. 13 is a portion of a Smith chart 128 showing the simulation forfifteen different capacitor values 129 measured at 13.56 MHz, and theirresponse 130 over frequency. It is shown that, as the frequency shifts,the impedance shifts towards the nearest point, filling in the arc.

This was noteworthy, because it indicates that the change in impedancecaused by an increase or decrease in percentage of capacitance isequivalent to the change in impedance due to an increase or decrease inpercentage of frequency, as one would expect in view of Equation 1below.

$X_{c} = {\frac{1}{2\pi*\Delta\%{freq}*C} = \frac{1}{2\pi*fr{eq}*\Delta\% C}}$

Further, one could say that this is similar to adding or removing ashunt capacitor in parallel to the variable capacitor. The capacitor inparallel with the variable capacitor could be considered part of theload, as it is attached to the same node.

Thus, it can be assumed for a one-dimensional match that the change incapacitance due to frequency is equivalent to a change in the load,having a capacitor at the input shunt leg. When running in auto-tunemode, the match would see this change in frequency as a change in theload. Thus, if the load changes by a certain percentage due tofrequency, the variable capacitor would adjust by a proportionatedifference but in the opposite sign to counteract the change inimpedance.

The next step was to look at the matching algorithm and how it wouldreact to changes in frequency. To do this, the one-dimensional matchcircuit was simulated at three different frequencies, 13.56 MHz and at±5%, and with 169 different capacitor values ranging from 290 pF to 1910pF. The Z-Parameters were calculated for each combination, and then thebest matching capacitance table was generated by inputting a differentload impedance with each set of Z-Parameters and finding which positionhad the lowest gamma for each load at each frequency.

The next step was to use a list of various input impedances and theZ-Parameters to calculate different load impedances for each frequencyat different capacitor positions. For example, when the variablecapacitor is at 50%, and the input impedance is determined to be 20+j0Ω,the load impedance for each frequency can be calculated. Thesecalculated load impedances are then used to find the best match positionon the lookup table.

Since the V/I sensor has little change when the frequency is swept, wecan assume the input impedance reading would not be affected by itchanging. The V/I sensor also assumes that the frequency is 13.56 MHz.To measure the accuracy of the match over frequency, the best matchcapacitor percentage will be compared to the other two frequenciesfinding their perspective best matches for their calculated loads. So,at 50% capacitance and an input impedance of 20+j0Ω, the 13 MHz matchwill have a load of 4.9+j10.3Ω, the 12.88 MHz will have a load of5.5+10.6Ω, and the 14.24 MHz will have a load of 4.4+j10.0Ω. Multipleinput impedances were randomly picked and their data can be found belowin Table 2.

TABLE 2 Frequency versus Best Match Capacitor Position Capacitor InputStart Capacitor End Position Impedance Position 12.88 MHz 13.56 MHz14.24 MHz 20 + j0  25.0% 11.3% 11.9% 11.9% 20 + j0  50.0% 36.3% 36.9%36.9% 20 + j0  75.0% 61.9% 61.9% 61.9% 50 + j50 25.0% 36.3% 35.7% 35.7%50 + j50 50.0% 61.3% 60.7% 60.1% 50 + j50 75.0% 86.3% 85.1% 85.1% 50 −j50 25.0% 20.8% 21.4% 21.4% 50 − j50 50.0% 45.8% 46.4% 47.0% 50 − j5075.0% 70.8% 72.0% 72.0% 200 + j0  25.0% 28.6% 28.6% 29.2% 200 + j0 50.0% 54.2% 54.2% 54.2% 200 + j0  75.0% 80.4% 79.8% 79.2%

As it can be seen in Table 2, the best match positions are extremelyclose to one another across frequency. The major source of error is fromquantization, where the load impedances were calculated to the nearest0.1Ω for the lookup table, and there are only 169 different capacitorpositions.

Testing was done with both the 400 kHz unit and the 13.56 MHz unit. TheS-parameters were measured and the best match table was calculated forspecified load impedance ranges. The unit was set to automaticallychange the capacitor position while the frequency was varied manually.For the 400 kHz unit, the load was again set to 45-j372Ω. The matchedcondition was at frequency 417 kHz, 100 Hz higher than the manuallytuned test, and a capacitance of approximately 12,428 pF, one fine capposition more than in the manually tuned test, giving a VSWR of 1.04:1.The 13.56 MHz match was also tuned to its load. The matched conditionwas at frequency 13.98 MHz, which was 10 kHz less than the manuallytuned test, and the capacitance was about 435 pF, one fine positionhigher than the manually tuned test. This gave a VSWR of 1.07:1.

It was concluded that a one-dimensional EVC match with variablefrequency sweep tuning was capable of working. With the input V/I sensorand two-port network parameters, the change in impedance due tofrequency was equivalent to a load with a change in an input shuntcapacitor. The tuning tables show that the variable capacitor's valuewill be the same at different frequencies for a given input impedance.The testing showed that the algorithm works with a manually adjustedfrequency.

Matching with Multi-Level Power Setpoints (Level-to-Level Pulsing)

In modern semiconductor processes, there are instances where the processrequires the RF source to generate a multi-level pulse signal such thatthe RF signal has cyclically recurring pulse intervals with differingamplitude levels. In some cases, the change in the power setpointamplitude level can be very frequent and of the order of a few tens ofhundreds of microseconds. The multi-level power setpoint can be twolevels or more. Such pulsing is sometimes referred to as level-to-levelpulsing because the power setpoint goes from one level to another andnot just between a level and zero. While such cyclic adjustment of theintensity level of the RF energy used to generate the plasma can provideadvantages, it also creates challenges with regard to impedancematching, due to the rapid variations in the load impedance caused bythe differing pulse levels.

Typical RF matching networks based on electromechanical components, suchas vacuum variable capacitors, cannot move their positions for the shortpulses of level-to-level pulsing, and therefore they are set to (ortheir internal automatic matching algorithms set themselves to) anaverage position for the electromechanical components setting. This isnot an optimal method, since the electromechanical matching network isnot tuned to either one level or the other and thus the RF source in thesystem is exposed to high reflected power for each of the levels.

An RF matching network utilizing solid state technology, which mayinclude the use of EVCs, is able to tune significantly faster, and thusis able to match for each of the power setpoint levels. The methodsdescribed below provide methods for performing RF impedance matchingwhen the RF signal has multi-level power setpoints. The methods can beapplied to various types of RF matching networks based on solid statetechnology, including as those matching networks discussed above thatutilize one or more EVCs.

FIGS. 14 and 15 are discussed below to describe an embodiment forperforming level-to-level pulsing. In the exemplified embodiment, twonon-zero pulse levels are utilized. The invention is not so limited,however, as any number of two or more pulse levels may be used. Further,the exemplified embodiment measures the parameters voltage, current, andphase at the RF input, and generates running parameter-related values(described below) based on these values, but the invention can measureany parameter (one or more) related to the load, and make thatmeasurement at other locations in the system (e.g., the RF output of thematching network), and base the parameter-related values on any of thosedifferent parameters.

FIG. 14 provides a flow chart of the exemplified process 300 forimpedance matching when the RF input signal has multi-level powersetpoints. FIG. 15 provides a graph 330 of RF signal 332 having a firstpulse level L1 and second pulse level L2, as well as the times 338, 339for determining the parameter-related value. In the exemplifiedembodiment, the pulse level changes periodically at a pulse levelinterval 333, 334.

Returning to FIG. 14, the control circuit of the matching networkdetects whether the first pulse level is being provided (operation 302).If so, the control circuit measures the parameter related to the loadfor the first pulse level (operation 304), which in this embodimentincludes the voltage (V), current (I), and phase (Φ) at the input of thematching network (see parameters 336 in FIG. 15). These values can bemeasured independent of the RF source, or the system can synchronizesampling with when the RF source samples them. Based on the measuredparameter, the control circuit will determine a parameter-related valuefor the first pulse level (operation 306), which will be used to alterthe EVC (operation 308), provided the control unit determines that analteration to the EVC is warranted.

The parameter-related value can be any value based on the one or moremeasured parameters. In its simplest form, the parameter-related valuemay be the measured parameter(s) itself. In the exemplified embodiment,however, the parameter-related value is based on previously-determinedparameter-related values. Specifically, the new parameter-related valueis an average of the current measured parameter and a predeterminednumber of previously-determined parameter-related values. For example,at the last time of times 338, the parameter-related value is theaverage of the parameter value at the last time of times 338 (thecurrent time) and the parameter-related values determined at the firstthree times of times 338 (the previous three times). In otherembodiments, other methods of using prior parameter-related value(s) maybe used.

In the exemplified embodiment, the parameter-related value is used tocalculate the input impedance at the RF input of the matching network(Z_(input low)). In other embodiments, other values can be determined,such as the reflection coefficient at the RF input of the matchingnetwork (Γ_(input low)). The exemplified system uses the calculatedinput impedance (Z_(input low)) (or related value such as Γ_(input low))and the matching network's parameter matrix (such as one of theparameter matrices discussed above) to determine the load impedance(Z_(output low)). The system next uses the determined load impedancealong with the desired input impedance at the input of the match(typically 50+j0) to determine the best configuration for the EVCs ofthe matching network—that is, to determine the best positions for thediscrete capacitors of the EVCs (EVC1_(low1) and EVC2_(low2)). In theexemplified embodiment, the matching network uses two EVCs, though inother embodiments more or less EVCs can be used. In another embodiment,the system could alter one or more EVCs in conjunction with altering anRF frequency, thus using a combination of capacitor tuning and frequencytuning. In this embodiment, the system will determine both the best EVCconfiguration and the best RF frequency value (e.g., EVC1_(low1) andfreq_(low1)). In the exemplified embodiment, the matching network nextchanges the EVCs to their new configurations. Accordingly, EVC1 ischanged to the EVC1_(low1) position, and EVC2 is changed to theEVC2_(low2) position. In other embodiments, other configurations may beused, such as changing to EVC1_(low1) and freq_(low1). Note that theinvention is not limited to the method for determining a match impedancediscussed above. One or more of these steps may be omitted betweendetermining the parameter-related value and the match configuration,and/or be substituted with another step for ultimately determining thenew match configuration. For example, while the foregoing embodimentsperformed matching based on input impedance or a reflection coefficient,in other embodiments matching can be performed based on alternativevalues, such as maximum delivered energy during a pulse or minimum lossof energy during a pulse. Further, matching can be based on RF inputphase and/or magnitude errors, on the measured reflected power, or on aload impedance measured directly at the output of the matching network.

Note that the system may include certain schemes that limit the extentto which the capacitor positions may be changed at a given time. Forexample, the alteration of the at least one EVC to provide the matchconfiguration may be prevented from being carried out until apredetermined time has passed since a previous alteration of the atleast one EVC. This scheme can ensure sufficient time has passed toallow the previous capacitor change to take effect. Further, in certaincircumstances, a protection scheme may allow one of the EVCs to changeto a newly determined position, but will not allow the other EVC (orEVCs) to move to a newly determined position (or positions). In otherembodiments, the protection scheme may prevent any number of changes tothe capacitor positions or frequency. In the exemplified embodiment, thechanges that are permitted by the protection scheme will be made, whilethe other capacitor positions (or RF frequency) will be held at itscurrent position (or frequency).

As shown in FIG. 15, during the first pulse interval 333, the controlcircuit will measure the parameter at several times 338 and repeat steps302-308 for each time 338, regularly updating the parameter-relatedvalue. In the exemplified embodiment, the times 338 (and times 339) forcalculating a new parameter-related value are separated by a timeinterval 340 that is 4 microseconds. In other embodiments, the timeinterval 340 can be of a different duration.

During first pulse interval 333, while a first level process 301A isbeing carried out, an independent second level process 301B is beingcarried out. While the first pulse level is being detected (operation302), the second pulse level is not being detected (operation 312).During this first pulse interval 333, while the first level process 301Ais measuring the parameter to determine the parameter-related value andalter the EVCs accordingly, second level process 301B is determining aparameter-related value for the second pulse level (operation 320)without measuring the parameter. This can be done by several methods. Inthe exemplified embodiment, presuming there were prior parametermeasurements when the second pulse level L2 was ON, theparameter-related value will be based on a predetermined number ofpreviously-determined parameter-related values. For example, the currentparameter-related value may be based on an average of a predeterminednumber of previously determined parameter-related values. For example,while when the pulse is ON the parameter-related value is the average ofthe currently measured parameter value and three previously-determinedparameter-related values, when the pulse is OFF the parameter-relatedvalue is the average of the four previously-determined parameter-relatedvalues. Thus, even when a given pulse level is OFF, a newparameter-related value can regularly be generated at each time interval340. The parameter-related value is not simply a previously measuredparameter value being held in memory until the pulse level is turnedback ON, but is a value (for each pulse level) being newly determined atregular intervals, even when a given pulse level is OFF, to create adata bus of values.

At second pulse interval 335, the first pulse level L1 is OFF and thesecond pulse level L2 is ON. When this occurs, the first pulse level L1and the second pulse level L2 switch roles. For the first pulse level(which is OFF), parameter-related values are determined at times 339without use of a newly measured parameter (operation 310), similar tothe process described with respect to operation 320 of the second-levelprocess. For the second pulse level (which is ON), parameter-relatedvalues are determined (operation 316) at times 339 using new parametermeasurements (314), and the at least one EVC is altered accordingly(operation 318). The different options for determining the parameter,the parameter-related value, and the match configuration apply to boththe first level process 301A and the second level process 301B.

The above-disclosed process for impedance matching during level-to-levelpulsing provides several advantages. There is no interruption incollecting parameter-related data, and the data set collected for eachpower level is practically continuous. As a result, the control loop canaccess this data at any time for determining new EVC and/or frequencysettings. Because in a preferred embodiment this data also relies uponaveraging the last few measured values, the disclosed method reduces thenoise and sudden measurement changes associated with stopping andstarting the measurement process. Further, the disclosed method ofdetermining parameter values for each level, irrespective of whether thelevel is ON or OFF, allows the control system to treat each level as ifit is its own matching network, thus increasing the flexibility andscalability of the control system to multi-level pulsing.

The above process may be carried out as part of a method ofmanufacturing a semiconductor. Such a manufacturing method may includeplacing a substrate in the plasma chamber configured to deposit amaterial layer onto the substrate or etch a material layer from thesubstrate; and energizing plasma within the plasma chamber by couplingRF power from the RF source into the plasma chamber to perform adeposition or etching. Further, the matching network described above mayform part of a semiconductor processing tool (such as tool 86 in FIG.3), the tool including the plasma chamber 19 and the matching network11A.

It is noted that, for the level-to-level pulsing discussed herein, thesystem may, for each of the pulse levels, carry out a separate matchingprocess based on determined parameter values for the pulse level. In oneexample where there are two pulse levels, the firmware may run a singlecontrol loop every 200 μs (or another predetermined time period) and,within each iteration of the control loop, the system may use twoseparate processing loops for the two pulse levels. There can be twodifferent match control structures, one per pulse cycle. Referencevalues upon which matching is based can be different for each of thepulse levels. Such differing reference values may include a reflectedpower value, a reflection coefficient, a time period for ignoring data,or a time period for holding a preset value. Programs may contain data,for example, as a single frequency match system with separate on/offpreset values for each of the pulse levels. When programs get loaded,the match structures for each pulse level can be populated with the sameset points, except the presets. Match tune logs may be populated in asingle data structure with entries for each pulse level with validitybits set appropriately. Tune logs may be printed to enable viewing pulselevel logs independently or, alternatively, the entries for each levelmay be printed one after another.

In another example where there are two pulse levels, the control loopmay run every 100 μs (or another predetermined time period) andalternate between pulse levels in those iterations instead of processingboth pulse levels in a single iteration. Thus, in this embodiment, theseparate matching processes of the different pulse levels are carried insequence one after another, each of the separate matching processesbeing carried out for a predetermined period of time. When there is nolevel-to-level pulsing, the system can speed up the processing cycletime for continuous wave mode to 100 μs by using this approach.

Switching Circuit for Electronically Variable Capacitor

FIG. 16 shows an embodiment of a switching circuit 640A for an EVC 651of a matching network according to one embodiment. In the exemplifiedembodiment, the EVC 651 is the EVC of FIG. 5, but the EVC is not solimited, as it can have any of the alternative features discussedherein, including a different number of discrete capacitors 653, anddiscrete capacitors of different values than those discussed withrespect to FIG. 5. Further, the EVC can form part of any type ofmatching network, including the various types of matching networksdiscussed herein. The exemplified matching network is coupled between anRF source and a plasma chamber, as shown, for example, in FIGS. 1-3.

The exemplified EVC comprises a plurality of discrete capacitors 653A,653B coupled to a first terminal 613. Each discrete capacitor 653A, 653Bhas a corresponding switch 661A, 661B configured to switch in (or “ON”)the discrete capacitor and switch out (or “OFF”) the discrete capacitorto alter a total capacitance of the EVC 651. In the exemplifiedembodiment, the switch 661A is in series with the discrete capacitor653A, but the invention is not so limited. Further, in the exemplifiedembodiment, the switch 661A is a PIN diode, but the invention is not solimited, and may be another type of switch, such as a NIP diode. In yetother embodiments, the switch may be a MOSFET, a JFET, or another typeof switch. Further, in the exemplified embodiment, the PIN diode has acommon anode configuration such that the anode of each PIN diode 661A,661B is coupled to a ground 630, which may be any common node. Theinvention is not so limited, however, since in other embodiments the EVCmay use a common cathode configuration such that the cathode of each PINdiode is coupled to the ground 630 (and the components of the drivercircuit are altered accordingly). Further, it is noted that two or moreswitches may be used in series to increase the voltage rating and/or twoor more switches may be used in parallel to increase the current ratingof the channel.

Each PIN diode switch 661A, 661B has its own switching circuit 640A,640B, which is connected to a control circuit 645. Switching circuit640B is shown as including switch 661B, filter 641B (which may besimilar to the filter circuits 37, 41 discussed above), and drivercircuit 639B. Filters 641A, 641B can be, for example, an LC circuitsimilar to filter circuit 9 of U.S. Pat. No. 10,340,879, or the filtercircuit beside output 207 in FIG. 6A of U.S. Pat. No. 9,844,127. Each ofthese patents is incorporated herein by reference in its entirety.

Exemplified switching circuit 640A has the same components as switchingcircuit 640B, but shows the driver circuit 639A in greater detail. Thedriver circuit 639A may be integrated with the PIN diode 661A (or othertype of switch), or may be integrated with the discrete capacitors ofthe EVC of the matching network. One of skill in the art will alsorecognize that certain components of the driver circuit 639A may bereplaced with other components that perform the same essential functionwhile also greater allowing variability in other circuit parameters(e.g., voltage range, current range, and the like).

The exemplified driver circuit 639A has two inputs 605A-1, 605A-2 forreceiving control signals from the control circuit for controlling thevoltage on the common output 607A that is connected to and drives thePIN diode 661A. The voltage on the common output 607A switches the PINdiode 661A between the ON state and the OFF state, thus also switchingin/ON and out/OFF the discrete capacitor 653A to which the PIN diode661A is connected. The state of the discrete capacitor, in thisexemplary embodiment, follows the state of the corresponding PIN diode,such that when the PIN diode is ON, the discrete capacitor is alsoin/ON, and likewise, when the PIN diode 661A is OFF, the discretecapacitor is also out/OFF. Thus, statements herein about the state ofthe PIN diode 661A inherently describe the concomitant state of thecorresponding discrete capacitor 653A of the EVC 651.

In a preferred embodiment, each of the first power switch 611A and thesecond power switch 613A is a MOSFET with a body diode, though in otherembodiments either of the power switches can be another type of switch,including any other type of semiconductor switch. The invention mayutilize a variety of switching circuit configurations. For example, theinvention may utilize any of the switching circuits disclosed by U.S.Pat. No. 9,844,127, such as those shown in FIGS. 3, 6A, 6B, and any ofthe switching circuits disclosed by U.S. Pat. No. 10,340,879, such asthe switching circuit shown at FIG. 18. As stated above, each of thesepatents is incorporated by reference in its entirety.

In the exemplified embodiment, a high voltage power supply 615A isconnected to the first power switch 611A, providing a high voltage inputwhich is to be switchably connected to the common output 607A. A lowvoltage power supply 617A is connected to the second power switch 613A,providing a low voltage input which is also to be switchably connectedto the common output 607A. In the configuration of the driver circuit639A shown, the low voltage power supply 617A may supply a low voltageinput which is about −3.3V. Such a low voltage, with a negativepolarity, is sufficient to provide a forward bias for switching the PINdiode 661A. For other configurations of the driver circuit 639A, ahigher or lower voltage input may be used, and the low voltage input mayhave a positive polarity, depending upon the configuration and the typeof electronic switch being controlled.

In the exemplified embodiment, the control circuit provides separatecontrol signals to separate inputs 605A-1, 605A-2 of the driver circuit639A. In this embodiment, the separate inputs 605A-1, 605A-2 are coupledto the first and second power switches 611A, 613A, respectively. Thecontrol signals to the separate inputs may be opposite in polarity. In apreferred embodiment, the first and second power switches 661A, 613A areMOSFETS, and the separate control signals go to separate drivers forpowering the MOSFETs. In an alternative embodiment, the control circuit645 provides a common input signal. The common input signal mayasynchronously control the ON and OFF states of the first power switch611A and the second power switch 613A, such that when the first powerswitch 611A is in the ON state, the second power switch 613A is in theOFF state, and similarly, when the first power switch is in the OFFstate, the second power switch 613A is in the ON state. In this manner,the common input signal controls the first power switch 611A and thesecond power switch 613A to asynchronously connect the high voltageinput and the low voltage input to the common output for purposes ofswitching the PIN diode 661A between the ON state and the OFF state. Theinvention, however, not limited to such asynchronous control.

The inputs 605A-1, 605A-2 may be configured to receive any type ofappropriate control signal for the types of switches selected for thefirst power switch 611A and the second power switch 613A, which may be,for example, a +15 V control signal. In a preferred embodiment, thedriver circuit has a separate driver for driving each of the first powerswitch 611A and second power switch 612A. In another embodiment, thefirst and second power switches 611A, 613A are selected so that they mayreceive a common input signal.

In the exemplified embodiment, a power supply 618 is coupled to an inputof the low voltage power supply 617A. In a preferred embodiment, thepower supply 618 provides 24 VDC. The invention, however, is not solimited, as other power supplies may be utilized.

In the exemplified embodiment, when the second power switch 613A is ON,a current 663A flows between the PIN diode 661A and the low voltagepower supply 617A. At the same time, current flows from the power supply618 to the input of low voltage power supply 617A, and to the ground630. A sensor may be positioned at a node of the switching circuit 640Ato measure a parameter associated with the current 663A flowing betweenthe low voltage power supply 617A and the PIN diode switch 661A. In theexemplified embodiment, sensor 664A is positioned at an input of the lowvoltage power supply 617A, and measures the current 667A flowing intothe input from the power supply 618, which is related to current 663A.In other embodiments, the sensor can be at other positions in theswitching circuit 640A, such as at node 665A (the output of the lowvoltage power supply) or node 666A (the anode of PIN diode 661A) or inthe path of the filter 641A between the driver circuit and the switch(e.g., driver output 607A or the output of filter 641A). In theexemplified embodiment, the parameter is the value of the currentflowing at the node, but in other embodiments the parameter measured maybe any parameter (including voltage) associated with current flowingthrough the switch or switches. In yet other embodiments, the parameteris any parameter associated with the driver circuit.

EVC Diagnostic System and Method

EVC-based impedance matching network units can fail for various reasons,during testing or even in the field. It would be beneficial if amatching unit could provide detailed feedback as to why it was notoperating. The system and method discussed below discloses an embodimentof an automated self-diagnostic function that an impedance matchingnetwork can run to give more information when a problem arises, and/orcan run at bootup.

The most common failure that a matching network unit will see occurswith the driver of a switch for an EVC. The bottom switching element(e.g., second power switch 613A coupled to the low voltage powersupply), the top element (e.g., the first power switch 611A coupled tothe HVDC 615A), or even both can fail. Occasionally, more than onedriver channel will fail. Less likely, PIN diodes have failed, while thedriver is fine. There have also been cases where an assembly issueoccurred or an unforeseen circumstance from shipping, causing a switchto not operate properly, which is usually from a loose connector.Another potential problem is a failed power supply. Although thistypically comes with a driver failure, a failed power supply is apossibility, especially when the unit is first turned ON.

For the self-diagnostic test described herein to operate, the matchingunit will need to have integrated hardware (e.g., sensors) to measuredifferent parameters. These measurements may include anything vital tothe operation of the matching unit, such as voltage monitors for eachpower supply, a current sensor for measuring bias current, a sensor formeasuring fan speed from its tachometer output, and a sensor or othermeans to determine that all the interlocks are closed. Once implemented,these measurements are calibrated, if necessary, and have somepredefined pass-fail criterion.

FIG. 17 is a flow chart for a method 700 for performing diagnostics on amatching network according to one embodiment. In operation 702, thematching network is turned ON. In operation 704, the system checks forany faults that are not related to the driver circuit, such as fans,interlock, issues with any calibration data or parameters, etc. This maybe checked when the unit boots up and be constantly checked while theunit is operating. If any of these faults occur, the unit should warnthe user of a system error (operation 706) before running aself-diagnostic test.

Since the self-diagnostic test will most likely be run after a failure,turning ON the driver circuit's high voltage power supply (such as highvoltage reverse-biasing supply 615A, referred to as “HVDC”) should beavoided initially to prevent further damage to the matching unit. Theother power supplies (e.g., low voltage (forward biasing) power supply617A and power supply 618), however, are capable of testing most of thefunctionality of the unit. In operation 708, these other power suppliesare enabled. In operation 710, it is verified that these power suppliescan all be powered ON. If any supplies do not turn ON (and/or a voltagefor any of the supplies is not in a predetermined range) the test willbe terminated, and the unit will alert the user which supply or supplieswere not functioning properly (operation 712).

In operation 714, a lower driver test is performed. An embodiment of adriver test method 750 is provided in FIG. 18. In operation 752, all theswitches of the driver circuit are turned OFF (e.g., switches 661A, 661Bof driver circuit 639A), thus switching out all the discrete capacitorsof the plurality of discrete capacitors of the EVC. In operation 754, asensor at a first node measures a parameter associated with a currentflowing between a power supply of the switching circuit and one or moreof the switches of the discrete capacitors. Referring to FIG. 16, in theexemplified embodiment, the sensor may be positioned at node 664A, whichis at an input of the low voltage (and forward bias) power supply 617A,and measures the current 667A flowing into the input from the powersupply 618, which is associated with current 663A flowing between thelow voltage power supply 617A and PIN diode switch 661A. It is notedthat the a relationship between current 663A and current 664A is suchthat (assuming the low voltage power supply 617A is 100% efficient orloss less) the current at 667A would be the voltage of the low-voltagepower supply 617A (e.g., 3.3V) divided by the voltage of the powersupply 618 (e.g., 24), multiplied by current value of current 663A. Inother embodiments, the node can be at other positions in the switchingcircuit 640A, such as at node 665A (the output of the low voltage powersupply) or node 666A (the anode of PIN diode 661A) or in the filter pathbetween the driver circuit and the switch (e.g., output 607A). In theexemplified embodiment, the parameter is the value of the currentflowing at the node, but in other embodiments the parameter measured maybe any parameter (including a voltage value) associated with currentflowing between a power supply and one or more of the switches 661A,661B of the discrete capacitors. In yet other embodiments, the parameteris any parameter associated with the driver circuit. The parametermeasurement at operation 754 value provides a baseline value for latercomparison.

In the exemplified driver test 750, the matching unit tests eachindividual bottom side (e.g., second power switch 613A), driver, filter,and PIN diode switch by switching them all from the OFF position to theON position individually. In operation 756, integer “i” is assigned thevalue of 1. Switch i (initially, switch 1) is then turned ON. Accordingto operation 760, the system may check for faults, such as ensuring thatthe power supplies are healthy by having a voltage monitor on each powersupply, and end the test if the power supplies are not healthy(operation 762). In operation 764, the parameter measured at operation754 is remeasured to determine a difference between the originalparameter value and the new parameter value. In operation 766, it isdetermined whether the difference between the initial parameter valueand the present parameter value (the “parameter delta”) is within apredetermined range. If it is not, it is indicated that switch i, itsdriver circuit, or its filter (the components of channel i) has failed(operation 768). At this stage, the test may stop or continue.

If the parameter delta is within range, the integer i is increased by 1(operation 770). If i is not greater than the total number of discretecapacitors (“iMax”) (operation 772), the next switch is turned on andsteps 760-770 can be repeated. Once all the discrete capacitors areswitched in, the test is complete (operation 774). The parametermeasurements at operation 764 allow the matching unit to know if eachchannel is working properly. After all the channels are tested, thematching unit can tell the user which channel(s) gave an error duringthe test. The parameter measurement can be done in two different ways,namely, either the switches are turned ON and left in the ON state asthe next switch is turned ON, or they are turned ON then turned OFF whenthe next switch is turned ON. If the switches are each turned OFF afterthe measurement, then the current measurement may be more accuratebecause there may be other factors that affect the measurement. Suchfactors could include the bias power supply's efficiency changing withthe load, the line drop from the cabling that delivers the bias voltageto the driver boards, which would also increase the bias voltage if theKelvin connection is implemented, or some other factor not mentioned. Italso allows for a single threshold to be used as a pass fail, which willreduce the chances of an error. It is noted also that in certainembodiments the predetermined parameter delta range can be differentdepending on which switches are being switched ON.

Returning to FIG. 17, if the lower driver test (operation 714)determines faults (operation 716), a driver error is output (operation718). If not, the HVDC is enabled (operation 720). All the channels andtheir switches should be in the ON position before turning ON the HVDC.This way, if there is a top side (e.g., first power switch 611A) driverfailure, the HVDC will not be given the opportunity to charge up,because it will be shorted to the negative bias. If this occurs, theunit can display “HVDC Too Low,” and the test can terminate.

In operation 722, the HVDC is checked to determine whether its voltageoutput is within a predetermined range. If not, an HVDC error isregistered (operation 723). If so, a full driver test with the HVDC ONis performed. Thus, the driver test 750 of FIG. 18 can once again beperformed (operation 724), but for when the HVDC is ON. Further, themeasuring and re-measuring of the parameter is a measuring and are-measuring of any parameter (e.g., current or voltage) associated witha current flowing between the high-voltage power supply and one or moreof the switches of the discrete capacitors. This can be measured, forexample, by a sensor in the current path. A fault may also be detectedby monitoring the voltage output of the HVDC, which will drop if one ofthe channels draws excessive current. If there are faults (operation726), a driver error is registered (operation 728).

The self-diagnostic test can further include switching all the driversON then OFF to verify that there are no issues with the most extremepossible switching condition (operation 730). If there are faults(operation 732), a driver error is registered (operation 734), and ifnot the test is complete (operation 736). It is noted that in otherembodiments, certain operations may be omitted and/or added.

Another self-diagnostic test would be to test whether the RF cavity orRF sensors were damaged during shipping or installation. This wouldrequire external hardware to be added to the unit, such as an RFgenerator at the input and a load of some sort. If the unit has a largesignal at the input, it could calculate what the output voltage shouldbe based on the input V/I-sensor and the measured S-parameters stored inthe unit. Since the units have an output voltage measurement, the unitcould compare the calculated value to the measured. If there is too muchof a discrepancy, the unit would trigger an alarm.

There are many benefits of internal testing. The biggest benefit is ifthe unit is damaged, the unit will be able to prevent other componentsor parts of the system from failing. The unit can also be repaired inthe field without additional test equipment. The technician could betold which PCB(s) and/or component(s) need to be replaced. Depending onthe failure, the unit could potentially be repaired without removing theunit from the tool. This is not possible when using certain testequipment, or if there is no indication on what the failure is.Depending on the damage, there is the possibility that the unit runs ina modified state. As an example, if a single channel is damaged, andthat channel can stay in the OFF state, and the matching unit couldavoid turning that channel ON. This would allow the user to continueproduction until the unit can be serviced.

It is noted that the above diagnostic method may form part of a methodof manufacturing a semiconductor. Further, a matching unit utilizing thediagnostic method may form part of a semiconductor processing tool,which further includes a plasma chamber for manufacturingsemiconductors.

Level-to-Level Matching with Pre-Pulse Capacitor Switching

Returning to the concept of level-to-level pulsing discussed above (seesection entitled Matching with Multi-Level Power Setpoints), a matchingnetwork typically has three modes of operation related to RF powerlevels: continuous wave, pulsing between non-zero and zero power levels,and pulsing between two non-zero power levels (level-to-level pulsing).Capacitor positions are not relevant when RF power is zero, so non-zeroto zero pulsing can be treated similarly to continuous wave. That is,the system can switch the capacitors at any time with respect to pulsestate and they will only affect RF power when it is non-zero. In thosetwo modes, the system calculates the best matching capacitor position(EVC configuration) and immediately switches the caps without regard tothe power level at that moment.

With level-to-level pulsing, however, plasma impedance can differsignificantly between the two RF power levels, and therefore appropriatecapacitor positions (EVC configurations) for the two power levels can bedifferent. The match in this mode switches the capacitors at thebeginning of each pulse state, that is, when the RF power level changes.The EVC configurations for each pulse level are independently calculatedduring one or more pulses and then automatically applied at the powerlevel change. This mechanism removes a need for synchronizing thecontrol loop with the pulse transitions. If pulses are long enough toaccommodate multiple capacitor switches, it may happen that a newcapacitor matching position is calculated and applied immediately ifappropriate, that is, there is no requirement to wait until the nextpulse change.

During level-to-level pulsing mode, RF power is on all the time, but foreach pulse level, power levels during pulse on and pulse off states aredifferent. This results in possibly different plasma impedances andconsequently different best capacitor positions (EVC configurations)during pulse on and off states. Ideally, the capacitors would be in theappropriate positions throughout the pulse on and off states.

A system can detect pulse state changes and trigger capacitor changes atthe moment of the pulse state change. The problem with this approach isthat the capacitor change (the switching of the EVC's discretecapacitors from one capacitor configuration to another) takes a non-zeroamount of time, typically, several microseconds. If the capacitorswitching is triggered at the moment of the pulse state change, theeffect of the new capacitor configuration will not be felt by plasma forsome time. In fact, the capacitor change may not be complete until nearthe end of the capacitor change interval.

To address this issue, the disclosed system is designed to predict whenthe next pulse state change will occur and initiate capacitor switchingto a new configuration before the pulse state changes. The initiation ofcapacitor switching can precede the pulse state change by about theduration of the time it would take for the capacitor switching to occur,thus causing the new capacitor configuration to coincide in time withthe pulse state change.

FIG. 19 is a flow chart for a level-to-level impedance matching method350 using such pre-pulse capacitor switching according to oneembodiment. In a first operation, the matching network is positionedbetween a radio frequency (RF) source and a plasma chamber (operation351). The RF source is configured to provide at least two repeating,non-zero pulse levels, the at least two pulse levels comprising a firstpulse level and a second pulse level. Note that any number of two ormore pulse levels may be used. The plasma chamber has a variableimpedance. Further, the matching network comprises at least oneelectronically variable capacitor (EVC) configured to switch between aplurality of match configurations for reducing a reflected power at anoutput of the RF source as the variable impedance of the plasma chamberchanges. As examples, the system may be any of the systems shown inFIGS. 1-3.

In the exemplified embodiment, the system determines, from among theplurality of match configurations, a new match configuration to be usedwhen there is an expected pulse level change from a first of the pulselevels to a second of the pulse levels (operation 352). In theexemplified embodiment, each EVC of the at least one EVC comprisesdiscrete capacitors configured to switch in and out to vary thecapacitance of the EVC and thereby provide the plurality of matchconfigurations. Thus, each “match configuration” comprises a positioningin or out for each of the discrete capacitors. Different matchconfigurations have different combinations of discrete capacitorsswitched in to provide different total capacitances.

The system then sends a control signal to alter the at least one EVC toprovide the new match configuration (operation 353). The control signalcan be any type of signal for causing, enabling, or helping enable thealteration of the EVC. The control signal is sent a predetermined timeperiod before a time for the expected pulse level change. Thispredetermined time period will be substantially similar to a time periodfor the EVC to switch between two match configurations of the pluralityof match configurations (e.g., 75-80 μsec). In this regard, a“substantially similar” time period is considered ±20% of the estimatedtime period for the EVC to switch between two match configurations ofthe plurality of match configurations. If the time periods are notidentical, it is preferred that the switching be completed after the newpulse has started, rather than before the new pulse has started.Further, it is noted that the importance of aligning the switchingcompletion and the pulse change varies with the duration of the newpulse. For example, if the pulse is only 100 μsec long for its RF ONperiod, then the alignment of the capacitor switch and the pulse change(and the similarity between the predetermined time period for switchingand the estimated time period for the EVC to switch) should be as closeas possible, such as ±10% or ±5%. On the other hand, if the pulse wassignificantly longer (e.g., 10 ms long), then there would be more leewayin aligning these times, such as ±20%.

The estimated time period can be obtained in a variety of ways. Forexample, this time period can be measured or calculated in advance.However the estimated time period is determined, the predetermined timeperiod will be chosen such that the switching is completed at or nearthe time of the pulse change. As shown in FIG. 19, the operations 352,353 may be repeated for a subsequent expected pulse level change.

There are different methods for determining the time for the expectedpulse change. For example, the method may include measuring a durationfor each of the pulse levels, and determining the time for the expectedpulse level change based on the measured durations for each of the pulselevels. Alternatively, a control circuit may receive from the RF sourceor from a semiconductor processing tool (e.g., from a pulse informationsignal), the durations of each of the at least two pulse levels, and astart time for one of the at least two pulse levels. From this data, thecontrol circuit may determine the time for the expected pulse levelchange.

The determination of the new match configuration may be accomplishedusing any of the means for determining a match configuration discussedherein. For example, the determination of the new match configurationmay be based on a value of the second pulse level and a measuredparameter related to the plasma chamber. The measured parameter valuemay be, for example, at least one of a voltage, a current, or a phase atan input of the matching network. Further, the determination of the newmatch configuration may be based on a parameter-related value and apreviously-determined parameter-related value. Further, the new matchconfiguration may be based on a load impedance value, which isdetermined based on an input impedance value at the input of thematching network or a reflection coefficient, which is determined basedon the measured parameter value. Further, the load impedance value maybe determined using a parameter matrix.

As indicated, the above process may be carried out by an impedancematching network, such as those shown in FIGS. 1-3. The matching networkmay include an RF input configured to operably couple to the RF source,and an RF output configured to operably couple to the plasma chamber,and the at least one EVC. A control circuit of the matching network maybe programmed to carry out the method discussed above and shown in FIG.19.

The above process may be carried out as part of a method ofmanufacturing a semiconductor. Such a manufacturing method may includeplacing a substrate in the plasma chamber configured to deposit amaterial layer onto the substrate or etch a material layer from thesubstrate, and energizing plasma within the plasma chamber by couplingRF power from the RF source into the plasma chamber to perform adeposition or etching. Further, the matching network described above mayform part of a semiconductor processing tool (such as tool 86 in FIG.3), the tool including the plasma chamber 19 and the matching network11A.

The above-described invention addresses the issue of delays in capacitorswitching and allows for better synchronization between capacitorswitching and pulse level changes, allowing the desired EVCconfiguration to be in place at the beginning of a new pulse level. As aresult, impedance matching is enhanced, reflected power is decreased,and efficiency in the delivery of RF power is improved.

Assigning Parameter Values to Different Activities

During impedance matching, control systems can continuously measureseveral signals. Some of those signals are useful for providing to auser interface, some for monitoring unit health, and some for matching.Further, some signals are useful for multiple functions. For example,voltage at the matching network's RF input may be useful both for unitprotection (health monitoring) and for matching.

Certain measurement signals are not reliable or usable for matching. Forexample, immediately after a pulse state change, the plasma is usuallyin a transient state, and therefore measurements taken during that timeare not useful for matching. Further, during capacitor switching, thematch may be for a moment in an unknown state and so correctinterpretation of some signals is impossible. Further, sometimes it maybe advantageous to only consider measurement signals from a short,predefined time interval for matching. Such a time constraint can createmultiple time intervals when measurement signals are valid for matching,while outside those intervals the signals are not valid for matching.Those invalid signals, however, may be useful for other purposes, suchas unit protection.

FIG. 20 is a flow chart for a method 360 of impedance matching whereparameter values are assigned to different activities according to oneembodiment. This method may be performed by a matching network having anRF input configured to operably couple to an RF source, an RF outputconfigured to operably couple to a plasma chamber, and at least oneelectronically variable capacitor (EVC) configured to carry out amatching activity of altering its capacitance to provide matchconfigurations (see, e.g., FIGS. 1-3). The matching network also mayinclude at least one device, each device outputting parameter signalsindicative of at least one changing value of a parameter related to theplasma chamber or the matching network. The device may be a sensoroutputting signals of a parameter value such as voltage, current, phase,or temperature. The sensors may be located, for example, at the RF inputor RF output of the matching network (see, e.g., sensors 41, 49 of FIGS.2 and 3). The device providing the parameter signal may alternatively beoutside the matching network. For example, the device may be the RFgenerator or the semiconductor processing tool that the matching networkforms part of. In this case, the parameter signal may be, for example, apulse information signal indicative of information about one or morepulses (such as a duration of a pulse, an amplitude of a pulse, and/or astart time of a pulse or pulse train).

According to method 360 of FIG. 20, a control circuit of a matchingnetwork (see, e.g., control circuit 45 of FIGS. 2 and 3, which maycomprise, for example, an FPGA) receives the parameter signals(operation 361). The control circuit then determines a parameter valuefor each parameter signal based on the parameter signal (operation 362).For each parameter value, the control circuit determines whether theparameter value is relevant to the matching activity of altering the EVCconfiguration (operation 363), and determines whether the parametervalue is relevant to a second activity of the matching network differentfrom the matching activity (operation 364). For example, as discussedabove, parameter values relevant to matching activity can be limited tothose output within a predetermined time interval, and thus excludethose values outside that time interval. Those excluded values, however,may still be used for the second activity. The method then carries outthe matching activity based on the parameter values determined to berelevant to the matching activity (operation 365), and carries out thesecond activity based on the parameter values determined to be relevantto the second activity (operation 366).

In one embodiment, the second activity is a protective action on behalfof a matching network, the RF source, or the plasma chamber, such asmonitoring for unsafe voltages or temperatures, and under certaincircumstances shutting down or limiting a function to protect the systemfrom damage. In another embodiment, the second activity can be providinginformation to a user interface. In yet other embodiments, differentvalues can be used for the three or more different activities (such asmatching, protective action, and user interface displaying). It is notedthat any parameter value can be considered relevant to one or more ofthe activities (or none of the activities). For example, RF inputvoltages taken within a certain time interval may be relevant to allactivities, while other RF input voltages may be relevant only toprotective action and/or display.

In one embodiment, the second activity is protective action on behalf ofthe matching network, the RF source, or the plasma chamber. Further, theparameter values relevant to the protective action comprise temperaturevalues, the temperature values not being relevant to the matchingactivity.

Further, similar to certain matching networks discussed above, thematching network may use level-to-level pulsing, where the matchingnetwork's RF input is configured to receive at least two non-zero pulselevels from the RF source. Where the second activity is protectiveaction on behalf of the matching network, the RF source, or the plasmachamber, the parameter values relevant to the protective action maycomprise at least one of (a) parameter values whose correspondingparameter signals were output immediately after a change between the atleast two pulse levels, (b) parameter values whose correspondingparameter signals were output during an altering of the at least oneEVC, and/or (c) parameter values whose corresponding parameter signalswere output outside a predetermined time interval.

The matching network may include any of the relevant features discussedabove. For example, each EVC may comprise discrete capacitors configuredto switch in and out to alter the capacitance of the EVC, each of thematch configurations comprising a positioning in or out for each of thediscrete capacitors. Further, each match configuration may be determinedbased on current parameter values determined to be relevant to thematching activity and previous parameter values determined to berelevant to the matching activity. Further, the parameter values maycomprise values of the measured parameter, or values derived from thevalues of the measured parameter. The term “parameter value” may referto any of “parameter values” or “parameter-related values” discussedherein. Further, in one embodiment, the determination of each matchconfiguration is based on a load impedance value, which is determinedbased on an input impedance value at the input of the matching networkor a reflection coefficient, which is determined based on an RF inputvoltage, the RF input voltage being a parameter value.

The above process may be carried out as part of a method ofmanufacturing a semiconductor. Such a manufacturing method may includeplacing a substrate in the plasma chamber configured to deposit amaterial layer onto the substrate or etch a material layer from thesubstrate, and energizing plasma within the plasma chamber by couplingRF power from the RF source into the plasma chamber to perform adeposition or etching. Further, the matching network described above mayform part of a semiconductor processing tool (such as tool 86 in FIG.3), the tool including the plasma chamber 19 and the matching network11A.

By assessing each parameter value and determining its relevance to eachof different purposes, the matching network can ensure it is using thebest data for each of its functions. This will allow for enhancedimpedance matching, while also ensuring protection of the system andreliable information.

Prioritization of Pulse Level

With level-to-level pulsing, the matching network may tune for a shortduration for a first pulse, and then tune again when the next pulse isinitiated. Depending on the period and duty cycle, this may require thematching network to switch continuously.

Commonly-owned U.S. patent application Ser. No. 16/778,181, filed Jan.31, 2020, is incorporated herein by reference in its entirety. FIG. 19of this application's shows a switching circuit for an EVC-basedmatching network. There is a discussion of the various challenges thatmay arise, including power dissipation caused by rapid, continuousswitching. The power dissipation will generate heat that can degradecomponents and reduce their lifetime. For the reasons discussed therein,and in U.S. Provisional Application No. 62/812,025 (incorporated byreference above) a preferred option for reducing power dissipation is toreduce switching frequency.

For level-to-level pulsing applications, the RF power is switchedbetween two power settings, e.g., a high power and a low power. Thefrequency, duty cycle, and power levels will have an effect on theplasma's impedance. There is even a difference in impedance between thehigh and low power states during pulsing. Thus, an EVC-based matchingnetwork may switch between two separate combinations of capacitors forboth pulse states to ensure maximum delivered power during the processand repeatability in tuning from run to run.

In an exemplified embodiment, a maximum switching frequency isdetermined. This can be done by a variety of means. For example, themaximum switching rate can be calculated based on the HVDC powersupply's maximum power delivery. In the following example, it is assumedthat temperature rise is not the limiting factor, which should be foundin testing as there are many factors that contribute to it. Theinvention, however, is not so limited. Further, various forms of testingmay be used to determine a maximum switching rate.

The minimum off-to-off period (period to switch a discrete capacitor inand then back out) can be calculated using the following equation. Inone example, the HVDC supply can deliver 23 W. There will be 50capacitors switching with 330 pF each. This gives a minimum period ofjust under 1 ms, or a maximum switching frequency of about 1 kHz. Thiswould be the limit for level-to-level pulsing.

$t = \frac{CV^{2}}{2P}$

This maximum level-to-level pulsing frequency, however, should not beused as the switching frequency. As in the case of a non-pulsingapplication, the unit could switch multiple times in a short period oftime, and if no tuned position is found, wait for a period of time as tonot discharge the power supply or over dissipate the various components.

If 2.1 ms is used as the time for the maximum number of switches fordischarging the HVDC supply, the unit can switch 42 times, or have 21off-to-off transitions. Giving some margin for the HVDC supply, a limitof 30 switches in a window of 15 ms can be implemented. If there are 50discrete capacitors as in the current example, this would result in aswitching limit of 1500 switches in 15 ms. This switching limit allowsthe matching network to tune in a short amount of time, as it rarelytakes more than a couple milliseconds to match. This is also the casefor normal on/off pulsing. The unit can switch during the on conditionas long as it follows the same limits as in the non-pulsing application.In the off condition, the HVDC supply will have the opportunity torecharge. It should be noted that the above numbers are examples and theinvention is not so limited.

The exemplified matching network is required to tune at both the highand low levels, and therefore reserves a minimum number of switches forthe pulse transitions. The exemplified matching network is alsoattempting to achieve the fastest possible match. In the exemplifiedlevel-to-level pulsing, knowledge of the pulsing frequency, duty cycle,and the maximum number of switches in a period of time are used, as wellas a way to synchronize the switching with the pulsing envelope. Withthis information the matching network can switch at the appropriatetimes and also maximize the number of additional switches to decreasethe tune time.

To find the maximum number of additional switches, the number ofreserved switches is determined, and can be calculated as two times theperiod, or the reciprocal of frequency. This is subtracted from themaximum number of switches in a period of time. The difference is nowthe new number of switches allowed in the same given amount of time. Thefollowing equation shows how to calculate the maximum number ofadditional switches, SW_(L2L_Max), where Sw_(Max) is the maximum numberof switches in the window, Sw_(Window) is the period of time where theswitches are counted, and f_(L2L) is the pulsing frequency. Thiscalculated value may then be rounded down to the nearest integer valueas to not exceed the maximum number of switches.

${Sw_{L2{L\_ Max}}} = {\left( {\frac{Sw_{Max}}{Sw_{Window}} - \frac{2}{f_{L2L}}} \right)*Sw_{Window}}$

At the maximum pulsing frequency, the number of reserved pulses is equalto the number of maximum pulses. So, the fastest way to tune in thissituation for each pulse state is to tune during pulse transitions. Asthe pulsing frequency is decreased, more switches become available.There are multiple tuning techniques that can be implemented.

A first strategy is to take the available number of switches and tunewhen needed. This is a first come, first served approach. A disadvantageof this is that for low frequency pulsing, all of the available switchescan be used up to tune one pulse state, and the other will only be ableto tune during transitions. Another strategy is to divide the availablenumber of switches between the pulse states. They can be divided evenlyor be weighted to some ratio to give priority to one state. This givethe advantage that both states will have the ability to tune quickly,and with the weighted, the more critical state can be tuned morequickly.

A final strategy gives priority to one of the pulsing states. Theadvantage of this is to allow the more critical state to be tuned first.For example, the high-power state may need maximum power delivery asquickly as possible, or the low power state is required to keep theplasma from flickering.

FIG. 21 is a flow chart for a level-to-level impedance matching method370 where a pulse level is prioritized according to one embodiment. In afirst operation, the matching network is positioned between the RFsource and the plasma chamber (operation 371). These components(matching network, RF source, and plasma chamber) can have any of thevarious features discussed herein. In the exemplified embodiment, the RFsource provides two repeating, non-zero pulse levels, one being thehigh-priority pulse level and the other being the low-priority pulselevel. In other embodiments, additional pulse levels may be included.The plasma chamber has a variable impedance, and the matching networkcomprises at least one EVC for providing an impedance match (see, e.g.,FIGS. 2-3). Similar to embodiments discussed above, the exemplified EVCcomprises discrete capacitors configured to switch in and out to vary atotal capacitance of the EVC and provide a plurality of matchconfigurations for reducing a reflected power at an output of the RFsource as the variable impedance of the plasma chamber changes.

In this embodiment, each EVC has a switching limit. The switching limitcomprises a predetermined number of switches in or out of the EVC'sdiscrete capacitors in a prior time interval of a predetermined time.For example, as discussed above, an EVC may have a limit such that itsdiscrete capacitors can only make 1500 switches (from in to out or fromout to in) in a 15 millisecond time interval. The invention is not solimited, however, as the limit can be any number of switches for anytime interval.

Returning to the exemplified method 370, the system determines aparameter value related to the plasma chamber or the matching network(operation 372), and determines a new match configuration for the atleast one EVC based on the determined parameter value (operation 373).These steps can be performed in any of the manners discussed herein.

The system may then determine whether the system has already reached theswitching limit (operation 374). If it has, the system may prevent thenext match configuration from being carried out and instead determinethe next match configuration (operations 372, 373). Note, however, thatoperation 374 is not required.

The system may further determine whether switching to the new matchconfiguration will cause an EVC to reach the switching limit (operation375). If not, the system may switch to the new EVC configuration(s)(operation 376). If so, the system then determines whether the new matchconfiguration is for the high-priority pulse level or the low-prioritypulse level (operation 377). If for the low-priority pulse level, thesystem prevents the switching of the at least one EVC to the new matchconfiguration. If for the high-priority pulse level, however, the systemswitches to the new match configuration (operation 376). As shown, theprocess (starting at operation 372) may then be repeated. In thisembodiment, there are only two pulse levels, and thus one ishigh-priority and one is low-priority. The invention is not so limited,as there may be more than two pulse levels. For example, if there werethree pulse levels, one could be high-priority and two could be lowpriority, or two could be high-priority and one could be low priority.It is only required that one of the pulse levels is given a higherpriority treatment in switching than one of the other pulse levels.

The number of discrete capacitors of an EVC that may be switched in orout may be limited based on pulse frequency. For example, there may be alimit of 5 discrete capacitors (each with a corresponding switch) thatmay be switched in or out for a 10 kHz level-to-level pulse frequency.If the determined match configuration requires more discrete capacitorsto switch in or out than are allowed by the limit, the high prioritystate can be held. The system may be designed such that switching onlyoccurs when the pulse state changes. Further, this limit on the discretecapacitors that may be switched in or out may be altered duringmatching.

In one embodiment, the higher-amplitude pulse level is the high prioritypulse. This may allow, for example, maximum power delivery as quickly aspossible. Alternatively, the lower-amplitude pulse level may be the highpriority pulse. This may, for example, help prevent the plasma fromflickering. It is further noted that the determination of the new matchconfiguration may be based on, in addition to the parameter value, anamplitude of an upcoming pulse level of the at least two pulse levels.

As indicated, the above process may be carried out by an impedancematching network, such as those shown in FIGS. 1-3. The matching networkmay include an RF input configured to operably couple to the RF source,and an RF output configured to operably couple to the plasma chamber,and the at least one EVC. A control circuit of the matching network maybe programmed to carry out the method 370 discussed above or a similarmethod.

The above process may be carried out as part of a method ofmanufacturing a semiconductor. Such a manufacturing method may includeplacing a substrate in the plasma chamber configured to deposit amaterial layer onto the substrate or etch a material layer from thesubstrate, and energizing plasma within the plasma chamber by couplingRF power from the RF source into the plasma chamber to perform adeposition or etching. Further, the matching network described above mayform part of a semiconductor processing tool (such as tool 86 in FIG.3), the tool including the plasma chamber 19 and the matching network11A.

Finally, it is noted that there is also the potential to tune withdisregard to the pulsing. In this case, the unit will switch until atune state is met, and hold that state until more switches becomeavailable. This process will continue until both states have a knowntune position. The disadvantage of this is, it will hold the tuneposition for a period of time which may cause a high reflected powerratio during the other pulse state. The advantage is, it will have thefastest possible tuning for the first state or the state that is givenpriority.

Restricted Switching Based on Blocking Voltage Value

As discussed with respect to FIG. 16, a switching circuit 640A for anEVC 651 of a matching network may include one or more power supplies615A, 617A. In the exemplified switching circuit 640A, the first powerswitch 611A and the second power switch 613A are configured toasynchronously connect the high-voltage power supply 615A and the lowvoltage power supply 617A to the common output 607A for purposes ofswitching the PIN diode 661A between the ON state and the OFF state, andthereby switching the corresponding discrete capacitor 653A in and out.

In the exemplified embodiment, high-voltage power supply 615A provides areverse-biasing DC voltage for the PIN diode switch 661A. This may bereferred to as a “blocking voltage” as it reverse-biases the PIN diode661A and thus prevents current from flowing, thus switching out itscorresponding discrete capacitor 653A. As used herein, the term“blocking voltage” will refer to any voltage used to cause a switch toswitch out or in its corresponding discrete capacitor. It is furthernoted that the switching circuit is not limited to that shown in FIG.16, but may be any circuit for switching in and out discrete capacitors,including those shown in U.S. Pat. No. 9,844,127, which is incorporatedherein by reference in its entirety.

In the exemplified switching circuit 640A, every time a switch 661A,661B switches for a discrete capacitor 653A, 653B of the EVC 651, theswitching pulls current from the high-voltage power supply 615A. If toomuch switching happens in a small period of time, the voltage level maydrop such that it may no longer provide sufficient voltage to providereverse-biasing of the switch. Thus, there is need for a method ofrestricting switching during impedance matching to prevent the blockingvoltage from becoming too low while still ensuring sufficient impedancematching to minimize reflected power.

FIG. 22 is a flow chart of a method 140 of impedance matching accordingto one embodiment. In a first step 141, the impedance matching networkis coupled between an RF source and a plasma chamber. The impedancematching network may include any of the features discussed herein, andshown, for example, in FIGS. 2-3. For example, the matching network mayinclude one or more EVCs comprising discrete capacitors andcorresponding switches, each switch configured to switch in and out oneof the discrete capacitors to alter a capacitance of the EVC. Further,the switches may be operably coupled to a power supply (such as HV powersupply 615A of FIG. 16) that is configured to provide a blocking voltageto the switches. As used herein, the term power supply may refer to asingle power supply or a collection of two or more power supplies.

A control circuit (which may comprise one or more circuits) determines anew EVC configuration for the discrete capacitors to provide a newcapacitance value that will enable impedance matching or at least reducereflected power (step 142). The control circuit may be, for example,control circuit 645 of FIG. 16, which is operably coupled to the EVC.Next, the control circuit (or a different control circuit) determines ablocking voltage value of the power supply (step 143). This value may bebased on a measured parameter related to the matching network (e.g., ameasured voltage at the discrete capacitors or their switches). Next,the control circuit determines whether the blocking voltage value is ator below a first voltage level (step 144). If the blocking voltage valueis not at or below a predetermined first level voltage, the system maycarry out the new EVC configuration for impedance matching without anylimitations on the discrete capacitors that may be switched (step 145).But if the blocking voltage value is at or below a predetermined firstlevel voltage, the control circuit may cause a limited altering of thecapacitance of the EVC (step 146). The limited altering may limit thenumber or type (or both number and type) of discrete capacitors toswitch in or out based on the extent to which the blocking voltage valueis at or below the first level. This limited altering may prevent thepreviously determined positioning of the discrete capacitors (forachieving an impedance match) from being fully carried out. This limitedaltering may be carried out in a number of ways, which will be describedin detail below.

Methods for Restricted Switching

In the following methods and examples, the relevant EVC of the matchingnetwork comprises fine and coarse capacitors (e.g., coarse capacitorseach have a capacitance at least twice as large as the capacitance anyone of the fine capacitors). The fine capacitors may be referred to asFine1, Fine2, Fine3, etc. A circuit monitors the output voltage level ofthe high voltage DC power supply. The system may prioritize limitingfine capacitors over limiting coarse capacitors, since limiting finecapacitors will generally have a lesser on the total capacitance of theEVC.

METHOD 1: In this method, the control software has multiple high voltageDC levels defined, such as:

DC Voltage Level Restrictions Level 0 No restrictions Level 1 RestrictFine1 switch Level 2 Restrict Fine1 and Fine2 switches Level 3 RestrictFine1, Fine2, and Fine3 switches . . . . . . Level n (minimum level)Restrict all switches

When the monitored voltage reduces to one of the above levels, then thecorresponding switch(es) are restricted from switching. Thus, as theblocking voltage value becomes lower, additional discrete capacitors areprevented from switching, until all discrete capacitors are preventedfrom switching. Put differently, when the blocking voltage value is ator below the first level, a first number of the discrete capacitors (onecapacitor in this example) is prevented from switching; and when theblocking voltage value is at or below a second level, the second levellower than the first level, a second number of the discrete capacitors(two capacitors in this example) is prevented from switching, the secondnumber being greater than the first number; and when the blockingvoltage value is at or below a third level, the third level lower thanthe second level, a third number of the discrete capacitors (threecapacitors in this example) is prevented from switching, the thirdnumber being greater than the second number, and so on. In otherembodiments, such as method 2 discussed below, the first, second, andthird number may increment by a number larger than one.

The voltage levels discussed herein (for this method as well as others)can be set to some calculated intervals (e.g., linear, quadratic, orexponential) or may be set with irregular intervals. The restrictionsdiscussed herein may cause slightly higher reflected power in the periodfollowing the restriction, but this will still be better thanrestricting all switches from switching, which could result in muchhigher reflected power.

The restriction algorithms discussed herein can be applied to continuouswave and pulsing modes, including multi-level pulsing (such aslevel-to-level pulsing as discussed herein). When it is applied tolevel-to-level pulsing case, the control algorithm can choose to applythe restriction to the lower power pulse state, so that the higher powerpulse state does not experience high reflected power.

Once a switching restriction is applied, the load on the high voltage DCpower supply is reduced and the voltage level of the high voltage DCpower supply starts increasing. When the voltage exceeds apre-determined restriction-release level, then the restricted switch isenabled and is free to switch as needed. The restriction-release levelcan be greater-than-or-equal-to the restriction level. Having itgreater-than will make it hysteretic, which may help reduce the limitingin subsequent steps.

METHOD 2: Restricted switching based on voltage level which reduces thenumber of capacitors to switch simultaneously with the step in therestriction being a value other than 1. This algorithm can be understoodas a “coarser” version of method 1, since more than one switch may benewly restricted when a new level is reached.

DC Voltage Level Restrictions Level 0 No restrictions Level 1 RestrictFine1 and Fine2 switches Level 2 Restrict Fine1, Fine2, Fine3, and Fine4switches Level 3 Restrict Fine1, Fine2, Fine3, Fine4, and Fine5 switches. . . . . . Level n (minimum level) Restrict all switches

METHOD 3: Restricted switching based on voltage level which reduces thenumber of capacitors to switch simultaneously:

DC Voltage Level Restrictions Level 0 No restrictions (X capacitors mayswitch) Level 1 X-1 capacitors may switch Level 2 X-2 capacitors mayswitch Level 3 X-3 capacitors may switch . . . . . . Level n (minimumlevel) X-X (zero) capacitors may switch

In this method, where there is a restriction in the number of capacitorsthat may switch and it must be decided which capacitor to switch andwhich to restrict, the capacitor with the lowest priority will berestricted from switching (Fine1 having the lowest priority andCoarseMax having the highest priority). For example, for the next tunecycle N capacitors are determined to switch for an impedance matching,but N−1 capacitors are allowed. Fine1 and Fine2 are not calculated toswitch, but Fine3 is calculated to switch. In this event, Fine3 wouldhold its position.

METHOD 4: Limit the number of switches to prevent a voltage drop byfinding a value close to the desired value. According to this method,one may prefer a “coarser” or less precise impedance matching than theEVC position calculated to cause less switching. For example, thelimited altering may prevent two fine capacitors from switching in favorof allowing one of the coarse capacitors to switch. Further, thediscrete capacitors switched in or out may be dependent upon thediscrete capacitors already switched in.

In one example, an accumulative setup (as described above) is used and“X” is the number of fine capacitors. The coarse and or fine capacitorsallowed to switch in is dependent upon the number of fine capacitorsalready switched in.

Determined EVC Position for Impedance Matching Allowed Switching Turn ONall fine capacitors If number of fine capacitors already ON is <X/2,increment to next coarse capacitor and turn OFF all fine capacitors Ifnumber of fine capacitors ON is ≥X/2; turn ON all fine capacitors TurnOFF all fine capacitors If number of fine capacitors already ON is <X/2,turn OFF all fine capacitors If number of fine capacitors ON is ≥X/2;decrement to next coarse capacitor and turn ON all fine capacitors

In another example, the fine capacitors increase in binary fashion suchthat the fine capacitors have capacitances that increase by about afactor of about two, where “about two” refers to a value of 1.5 to 2.5.In an ideal example where there are no parasitic capacitances, the finetune capacitors could increase by a factor of exactly two (e.g., 1 pF, 2pF, 4 pF, 8 pF). U.S. Patent Publication No. US2019/0272978 isincorporated by reference in its entirety. 4 fine capacitors (F1 to F4)create 16 potential positions for the 4 fine capacitors when combined.The following Position Table shows the 16 potential positions for thefine capacitors, where “x” is used to show that a capacitor has beenswitched in, and C1-C10 are the coarse capacitors.

Position Table Position C10 C9 C8 C7 C6 C5 C4 C3 C2 C1 F4 F3 F2 F1 0 1 x2 x 3 x x 4 x 5 x x 6 x x 7 x x x 8 x 9 x x 10 x x 11 x x x 12 x x 13 xx x 14 x x x 15 x x x x

In the following example, something similar to grey code is used to finda close value with the least number of switches. A new position formatching is calculated, but an alternative position is carried out thatprovides a similar capacitance with less switching.

Starting Calculated Position Position for Impedance Match PositionCarried Out Position 0 Position 3 Position 2 (turn on F2) or Position 4(turn on F3) Position 0 Position 7 Position 8 (turn on F4) Position 15Position 8 Position 7 (turn off cap 4)

In another example, a hybrid setup is used such that the coarsecapacitors are in an accumulative setup and the fine capacitors are in abinary setup. This example uses something like grey code to find a closevalue with the least number of switches or uses the closest coarseposition.

Starting Calculated Position Position for Impedance Match PositionCarried Out Position 0 Position 3 Position 2 (turn on F2) or Position 4(turn on F3) Position 0 Position 7 Position 8 (turn on F4) Position 15Position 8 Position 7 (turn off cap 4) Position 0 Position 15 Turn onnext coarse capacitor Position 15 Position 0 Turn off previous coarsecapacitor

METHOD 5: Limit the number of simultaneous switches to prevent a voltagedrop by finding a value close to (moving towards) the desired value. Inthe following examples, only one discrete capacitor changes per controlstep. This results in slower impedance matching (and thus potentiallygreater reflected power) but reduces the amount of switching to preventdrawing excessive current from the power supply.

In one example, the capacitors are in an accumulative setup. If theblocking voltage value must be increased, the fine capacitors areincremented until the desired value is reached. If the blocking voltagevalue must be decreased, the fine capacitors are decremented until thedesired value is reached.

In another example, the capacitors are in a binary setup. With eachcontrol step, the largest value is changed that gets closest to thedesired capacitor position without going past the value until thecalculated value is attained.

Starting Calculated Position Position for Impedance Match ActionsCarried Out Position 0 Position 3 Step 1: Turn on F2 and hold (Position2) Step 2: Turn on F1 (Position 3) Position 0 Position 7 Step 1: Turn onF3 and hold (Position 4) Step 2: Turn on F2 and hold (Position 6) Step3: Turn on F1 (Position 7) Position 15 Position 8 Step 1: Turn off F3and hold (Position 11) Step 2: Turn off F2 and hold (Position 9) Step 3:Turn off F1 (Position 8)

In another example, the capacitors are in a binary setup. The values arechanged such that the number of steps to the desired position is kept toa minimum with each control step until the calculated value is attained.

Starting Calculated Position Position for Impedance Match ActionsCarried Out Position 7 Position 8 Step 1: Turn off F1 and hold (Position6) Step 2: Turn off F2 and hold (Position 4) Step 3: Turn on F4 and hold(Position 12) Step 4: Turn off F3 (Position 8)

The above methods may be carried out as part of a method ofmanufacturing a semiconductor. Such a manufacturing method may includeplacing a substrate in the plasma chamber configured to deposit amaterial layer onto the substrate or etch a material layer from thesubstrate, and energizing plasma within the plasma chamber by couplingRF power from the RF source into the plasma chamber to perform adeposition or etching. Further, the matching network described above mayform part of a semiconductor processing tool (such as tool 86 in FIG.3), the tool including the plasma chamber 19 and the matching network11A.

Finding the Best Capacitor Position for Matching where Switching isRestricted

A solid-state RF matching network can use all solid-state components,such as solid-state variable capacitors (sometimes referred to herein aselectronically variable capacitors or EVCs). The solid-state capacitorscan vary their total capacitance by switching ON or OFF one or morediscrete capacitors. This process of varying capacitance by switchingdiscrete capacitors may be repeated multiple times until (or to ensure)the tuning criteria (usually a minimum input reflection coefficient orother parameter related to reflected power) is satisfied. As theswitching circuits switch multiple times to vary the capacitance, thedissipation in the switching circuit (e.g., in the driver circuit of aPiN diode-based switch) increases resulting in elevated temperatures forthose components. As discussed herein, one of the methods to control thedissipation in the switching circuit, and therefore its operatingtemperature, is to limit the number of times that switch can switch in agiven period. Once a switch exceeds this limit, all switching in the RFmatching network may be stopped and the matching network held in itscurrent state until a certain cooling period has passed. While such amethod prevents over-heating of the switch, it prolongs the RF tuningtime due to the switching hold that prevents the EVC from varying itscapacitance.

To cause an impedance match, a matching network's control circuit may beconfigured to calculate the best capacitor settings to satisfy the lowinput reflection coefficient criteria at the input of the match (or somesimilar criteria). This means, for example, making the RF matchingnetwork's RF input impedance as close to the RF output impedance of theRF source connected to its input. This impedance in most cases is 50+j0.In such a solid-state matching network, after the control circuit hasdetermined the best capacitor positions for the one or more EVCs, thediscrete capacitors of the EVCs are either switched ON or OFF to reachthe new positions. The problem with this approach is that switchingrestrictions (to prevent dissipation) may currently be in effect thatprevent certain discrete capacitors from switching, thus preventing thebest capacitor position from being implemented.

FIG. 23 is a flow chart of an impedance matching method 150 thataddresses this issue, finding the best capacitor position for impedancematching where switching is restricted. In a first step (step 151), animpedance matching network is operably coupled between an RF source anda plasma chamber (see, e.g., FIGS. 1-3). Using FIG. 3 as an example, thematching network 11A includes an RF input 13 configured to operablycoupled to the RF source, and RF output configured to operably couple tothe plasma chamber, and at least one EVC 31A, 33A. The exemplified EVCcomprises discrete capacitors and corresponding switches (see, e.g.,discrete capacitors 653 and switches 661 of FIG. 5) having differentpositions for providing different capacitances, each switch beingconfigured to switch in and out one of the discrete capacitors toprovide the different positions.

Next, the control circuit (e.g., control circuit 45 of FIG. 3)determines a parameter related to the matching network or plasma chamber(step 152). This can be any parameter that can be used to help determinethe best match position. The parameter may be any parameter, parametervalue, or parameter-related value discussed herein for impedancematching. In one embodiment, a sensor at the RF input detects one ormore RF signals and those signals are used to determine an inputreflection coefficient (a type of parameter).

Next, for the determined parameter, the control circuit determinespotential new positions for the EVC (step 153), the potential newpositions having differing effectiveness in causing an impedance matchbetween the RF source and the plasma chamber. In one embodiment, thecontrol circuit will rank the best capacitor positions from best tosuccessively worse, though this is not required. According to oneembodiment, to determine the preferred providing the greatesteffectiveness (or to rank the positions according to effectiveness) thecontrol circuit calculates, for each of the potential new positions, areflection parameter, the calculation of the reflection parameter beingbased on the determined parameter and the potential new position. Thereflection parameter can be any parameter indicative of reflected poweror the state of an impedance match (e.g., an input reflectioncoefficient or a reflected power value).

The method 150 further determines which of the discrete capacitors ofthe EVC are currently restricted from switching (step 154). There are avariety of means for deciding which switches may be restricted fromswitching, including those examples discussed herein. Most simply, oneor more switches may be restricted because a predetermined number ofswitching events have occurred in a predetermined period of time.Restriction may also be based on whether a predetermined cooling offperiod has elapsed for a switch that was previously restricted.

With the forgoing information, the method 150 determines a preferredposition for the EVC, the preferred position being the one of thepotential new positions that provides greatest effectiveness inproviding an impedance match while also not requiring, during execution,switching in or out of any of the discrete capacitors that are currentlyrestricted from switching (step 155). For example, returning to theembodiment where capacitor positions are ranked for effectiveness, thecontrol circuit may compare this list of best to successively worstmatch positions with the list of capacitor switches that are restrictedfrom switching. Based on the comparison of these two lists, the controlcircuit may select the best switching position that does not requireswitching a discrete capacitor that is restricted from switching. Inother embodiments, the match positions need not be ranked, but thecontrol circuit can nevertheless identify the best match positionavailable given any switching limitations.

The control circuit may further require that the preferred position hasa threshold effectiveness in providing an impedance match. This can bedone, for example, by determining whether the position in question willcause, in view of the determined parameter, a reflection parameter thatis unacceptable. In one embodiment, the reflection parameter may be aninput reflection coefficient or reflected power, and the system may beconfigured such that the preferred position cannot be a position thatwould cause a reflection parameter above a certain predetermined value.Further, this limit on the reflection parameter may be set by a user ofthe system. In other embodiments, other metrics may be used.

Finally, the control circuit causes the EVC to alter to the preferredposition by switching in and out the discrete capacitors as necessary(step 156).

It is noted that the above method may apply to any number of EVCs (orother variable reactance elements) in a matching network. For example,the matching network may comprise a second EVC that also has discretecapacitors restricted from switching at a given time. When determining apotential new positions, each new position can refer to a combination ofa new position for the first EVC and a new position for the second EVC.

It is further noted that, while the above embodiments discuss use of anelectronically variable capacitor, other types of variable reactanceelements may be used in their place. A variable reactance element caninclude one or more reactance elements, where a reactance element is acapacitor or inductor or similar reactive device.

The above methods may be carried out as part of a method ofmanufacturing a semiconductor. Such a manufacturing method may includeplacing a substrate in the plasma chamber configured to deposit amaterial layer onto the substrate or etch a material layer from thesubstrate, and energizing plasma within the plasma chamber by couplingRF power from the RF source into the plasma chamber to perform adeposition or etching. Further, a matching network using theabove-described method of impedance matching may form part of asemiconductor processing tool (such as tool 86 in FIG. 3), the toolincluding the plasma chamber 19 and the matching network 11A.

Controlling Power to Plasma Chamber

As discussed above, a solid-state RF matching network can vary acapacitance of an EVC by switching ON or OFF one or more discretecapacitors of the EVC. This process of varying capacitance may berepeated multiple times until the tuning criteria (e.g., a minimum inputreflection coefficient) is satisfied. In some semiconductor processes,the thickness of the deposited film or the depth of an etch step must becontrolled within an acceptable range over the surface of the wafer inthe plasma chamber. Certain conditions within the plasma chamber mayaffect the amount of material deposited or etched. These conditions mayinclude coating on the chamber walls. When the deposited film thicknessor etch depth exceeds a certain acceptable range, the processing must behalted, and the plasma chamber must be cleaned. This is typicallyincluded in the routine preventive maintenance. The increased frequencyor duration of preventive maintenance decreases the up time of thesemiconductor tool and has a negative impact on the throughput.

One way to overcome this variation in deposited film thickness or etchdepth is to vary the power delivered to the plasma chamber. For example,in one automated process, a measured parameter signal is provided to theRF source to allow the RF generator to alter its output power to affectthe power delivered to the plasma chamber.

In an alternative automated process, the matching network alters thepower delivered to the plasma chamber by altering the capacitance of thematching networks one or more variable capacitors. In a typical RFmatching network, the matching network's control system calculates thebest capacitor settings for providing an impedance match and thuslimiting reflected power. This is done, for example, by determining thebest capacitor position(s) to satisfy the low input reflectioncoefficient criteria at the input of the match. This usually meansmaking the matching network's RF input impedance as close to the RFoutput impedance of the RF generator connected to its input. Thisimpedance in most cases is 50+j0. In a typical matching network, afterthe control system has determined the best capacitor positions, thecapacitors are altered to reach the new positions.

FIG. 24 is a flow chart of a new impedance matching method 160 that, inaddition to performing impedance matching, also controls the powerdelivered to the plasma chamber, according to one embodiment. Accordingto this method, rather than simply using the best capacitor position forachieving an impedance match as is typically done, the control circuitdetermines a capacitor position that has a threshold matchingeffectiveness while also providing a desired RF power. In this way, thematching network can alter the power delivered to the plasma chamberwhile maintaining a reasonable impedance match at its input.

In a first step (step 161), an impedance matching network is operablycoupled between an RF source and a plasma chamber (see, e.g., FIGS.1-3). Using FIG. 3 as an example, the matching network 11A includes anRF input 13 configured to operably coupled to the RF source, and RFoutput configured to operably couple to the plasma chamber, and at leastone EVC 31A, 33A. The exemplified EVC comprises discrete capacitors andcorresponding switches (see, e.g., discrete capacitors 653 and switches661 of FIG. 5) having different positions for providing differentcapacitances, each switch being configured to switch in and out one ofthe discrete capacitors to provide the different positions.

Next, the control circuit (e.g., control circuit 45 of FIG. 3)determines a parameter related to the matching network or plasma chamber(step 162). This can be any parameter that can be used to help determinethe best match position. The parameter may be any parameter, parametervalue, or parameter-related value discussed herein for impedancematching. In one embodiment, a sensor at the RF input detects one ormore RF signals and those signals are used to determine an inputreflection coefficient or other parameter. In another embodiment, asensor at the RF output detects one or more RF signals and those signalsare used to determine an input reflection coefficient or otherparameter.

Next, the control circuit determines, based on the determined parameter,potential new positions for the EVRE that would have a thresholdeffectiveness in providing an impedance match between the RF source andthe plasma chamber (step 163). This can be done, for example, bydetermining whether the position in question will cause, in view of thedetermined parameter, a reflection parameter that is unacceptable. Inone embodiment, the reflection parameter may be an input reflectioncoefficient or reflected power, and the system may be configured suchthat the preferred position cannot be a position that would cause areflection parameter above a certain predetermined value. Further, thislimit on the reflection parameter may be set by a user of the system. Inother embodiments, other metrics may be used.

Further, the exemplified method 160 determines a preferred position forthe EVC (step 164). This is done by determining which one of thepotential new positions meeting the threshold effectiveness has anefficiency in delivering RF power from the RF input to the RF outputthat would cause an RF power at the RF output to be closest to a desiredRF power. In one embodiment, the control circuit determines ranks theacceptable capacitor positions (those satisfying the thresholdeffectiveness) from best to successively worst efficiencies. Theseefficiencies determine how much of the RF power at the input of thematching network is delivered to the output of the matching network. Forexample, efficiency may be understood as output power divided by inputpower. The control circuit's algorithm then selects an appropriatecapacitor value setting based on the efficiency that would alter theamount of power delivered to the output of the match to the desiredpower. The invention, however, is not limited to this embodiment. Forexample, it is not required that the capacitor positions be ranked.Rather, the control circuit may simply identify the position thatprovides the desired efficiency.

There are various methods for determining the efficiency of potentialnew positions in delivering RF power from the RF input to the RF outputof the matching network and adjusting the capacitor positionaccordingly. To provide automated control, a correlation may bedeveloped between the deposited film thickness or the etch depth and oneof the measured parameters associated with the plasma chamber(chamber-related parameter). This parameter could be the DC voltagedeveloped in the plasma and fed back to the output of the matchingnetwork. This parameter could also be the RF output current or the RFoutput voltage, or any number of other parameters associated with thematching network. In one embodiment, the control circuit determineswhich of the potential new positions would cause the chamber-relatedparameter to a achieve a value closest to a value associated with apredetermined deposited film thickness or an etch depth.

In certain embodiments, the control circuit may calculate, for each ofthe potential new positions meeting the threshold effectiveness, aresulting RF power at the RF output. The calculation of the RF powerwould be based on the determined parameter and the potential newposition. These calculations could be used to determine the potentialnew position that would result in an RF power closest to the desired RFpower.

It is noted that in certain embodiments, the preferred position may alsobe limited to those positions that would not require switching in or outof any of the discrete capacitors that are currently restricted fromswitching. Discrete capacitors may be limited for a variety of reasons.For example, as discussed above, switching restrictions may be made toprevent dissipation and increased temperatures. A determination of whichof the discrete reactance elements of the VRE are currently restrictedfrom switching is made based, for example, on whether any of thediscrete capacitors has previously switched a predetermined number oftimes in a predetermined period of time.

Finally, the control circuit causes the EVC to alter to the preferredposition by switching in and out the discrete capacitors as necessary(step 165).

The disclosed methods provide advantageous means for a matching networkto ensure that a desired power is delivered to the plasma chamber,thereby keeping the thickness of the deposited film or the depth of theetch step within an acceptable range over the surface of the wafer inthe plasma chamber. By enabling a more uniform deposited film thicknessor etch depth from wafer to wafer, the preventive maintenance cycle willbe extended, thus prolonging uptime and throughput.

It is noted that the above method may apply to any number of EVCs (orother variable reactance elements) in a matching network. For example,the matching network may comprise a second EVC that also has discretecapacitors restricted from switching at a given time. When determining apotential new positions, each new position can refer to a combination ofa new position for the first EVC and a new position for the second EVC.

It is further noted that, while the above embodiments discuss use of anelectronically variable capacitor, other types of variable reactanceelements may be used in their place. A variable reactance element caninclude one or more reactance elements, where a reactance element is acapacitor or inductor or similar reactive device. A variable reactancemay be, for example, a variable capacitance or a variable inductance.Further, the reactance elements used need not be electronically variable(solid state). Rather, the above methods may apply, for example, to amatching network comprising electro-mechanical components, such asmechanically variable capacitors (e.g., vacuum variable capacitors) orvariable inductors.

The above methods may be carried out as part of a method ofmanufacturing a semiconductor. Such a manufacturing method may includeplacing a substrate in the plasma chamber configured to deposit amaterial layer onto the substrate or etch a material layer from thesubstrate, and energizing plasma within the plasma chamber by couplingRF power from the RF source into the plasma chamber to perform adeposition or etching. Further, a matching network using theabove-described method of impedance matching may form part of asemiconductor processing tool (such as tool 86 in FIG. 3), the toolincluding the plasma chamber 19 and the matching network 11A.

Using Matching Network to Diagnose Plasma Chamber Characteristics

For semiconductor processes to run within optimal range, thesemiconductor manufacturing system requires periodic maintenance.Sometimes, this maintenance is preventive in nature before a componentfails. Other times, maintenance is performed if the process is slowlyshifting and would leave an acceptable range if not corrected. In termsof the RF power delivery system, the component that is in closestproximity to the plasma chamber is the RF matching network. Any changein the plasma chamber that impacts the RF characteristics of the chambercan be detected by the RF matching network. If detected at the matchingnetwork, the matching network can in turn alert the system that acertain process parameter is going out of range.

For purposes of describing the exemplified embodiments, reference willbe made to matching network 11A and semiconductor manufacturing system86 of FIG. 3. The invention, however, is not so limited. The exemplifiedmethod discussed below may be applied to a variety of matching networks,including solid state RF matching networks (e.g., those usingelectronically variable reactance elements such as EVCs), as well asmechanical fixed matching networks and different variable matchingnetworks.

RF matching networks may have sensors at the RF input and RF output. Forexample, in FIG. 3 see sensor 21 at RF input 13 and sensor 49 at RFoutput 17. Matching networks may also have sensors at certain nodeswithin the matching network. The sensor at the RF input may be (thoughis not limited to) a voltage, current, and phase detecting sensor(V/I/Phase sensor), a directional coupler, or a phase/magnitudedetector. The sensor at the RF output may be (though is not limited to)a V/I/Phase sensor, a directional coupler, a phase/magnitude detector,an RF peak voltage sensor, an RF current sensor, a DC voltage sensor, ora DC current sensor. The internal sensors can be, for example, voltagesensors across the one or more variable reactance elements (VREs) (e.g.,capacitors 31A, 33A) of the matching network, or current sensorsmeasuring current through a component of the matching network.

The RF matching network can keep a record of certain parameters, whichcan be analyzed by the RF matching network (e.g., by a control circuitsuch as control circuit 45) or provided to another component or systemto analyze. These parameters can include (but are not limited to) acurrent position of the VRE from among the possible positions of theVRE; a load impedance at the RF output of the matching network or at anode internal to the matching network; a matching tune time; a reflectedRF power or a reflection coefficient (input gamma) at the RF input ofthe matching network; a peak-to-peak voltage at the RF output of thematching network; a DC voltage at the RF output of the matching network;a DC current at the RF output of the matching network; or a phase angleof the load impedance at the RF output of the matching network.

FIG. 25 is a flow chart of a method 170 of using an impedance matchingnetwork to determine a plasma chamber characteristic, according to oneembodiment. Referring again to FIG. 3, in a first step 171, the matchingnetwork 11A is operably coupled between an RF source 15 and a plasmachamber 19. The matching network includes an RF input 13 configured tooperably couple to the RF source 15, an RF output 17 configured tooperably couple to the plasma chamber 19, and one or more variablereactance elements 31A, 33A, each VRE having different positions forproviding different reactances. In the exemplified embodiment, the oneor more VREs are two EVCs providing electronically variablecapacitances, though the invention is not so limited.

In step 172, reference values are determined or received for a parameterof the matching network. For example, the reference values could be avalid range of values for the parameter. The parameter can be anyparameter of the matching network, such as the parameters listed abovethat can be measured by the RF input, RF output, or internal sensors(e.g., voltage, current, and/or phase) or values (such as an impedancevalue) that can derived from one or more determined parameters. In otherembodiments, the parameter can be any parameter of the semiconductormanufacturing system.

In one embodiment, the valid range of values for the parameter is basedon values determined over a prior period of time of operation. Theparameter values may be, for example, an amount of current drawn by eachswitch of the VRE, the VRE being electronically variable; an amount ofcurrent drawn by at least one fan of the matching network; a number ofswitching operations by each switch of the VRE, the VRE beingelectronically variable; a number of motor reversals and a duration ofeach motor operation for a motor of the matching network, the VRE beingmechanically variable using the motor; an amount of DC or AC currentdrawn from an input power supply; and/or an AC or DC voltage at a pointinside the matching network. Such data can be used, for example, forpredicting a time for preventative maintenance prior to componentfailure. Using a range of valid parameter values, the matching networkcan predict when a component is operating outside its normal range orwill get outside its normal operating range and thus issue a warning tothe user with detail of the out-of-range reading, thus enabling thematch to be serviced before a failure occurs.

In certain embodiments, the valid range of values is learned by thematching network during a prior learning period using machine learningor another method for observing previous operations and determining aproper range. Exemplary methods for using a learning model are discussedbelow. For example, a user can set the matching network in learning modefor a certain period and during that period the matching network willlearn the valid ranges and not trigger an alarm or other indication of acharacteristic of the matching network. After the learning period ispassed, the matching network can then use the learned valid ranges tomonitor the process. The learning process can continue even after theinitial learning period has finished. In other embodiments, a user orother source (e.g., a separate processor or database), can provide thematching network with the valid range or other reference values.

Returning to FIG. 25, the method 170 further includes determining, basedon a signal from one of the sensors discussed above (at the RF input, RFoutput, or internal), a current value for the parameter of the matchingnetwork (step 173). Next, the method determines a characteristic of theplasma chamber based on the reference values and the current value (step174), and provides a visual or audible indication of the determinedcharacteristic of the plasma chamber, or causes an action to address thedetermined characteristic (step 175).

Where the reference values comprise a valid range of values for theparameter, the determination of the characteristic of the plasma chambermay be based on a determination that the current value is outside thevalid range of values. In response to determining the characteristic,the system may cause a visual or audible indication of the determinedcharacteristic (e.g., an alarm that the parameter is outside a range, ora message or digital indicator on a screen of the determinedcharacteristic). In addition or alternatively, the system may take anaction in response to the determined characteristic, such as altering aproperty of the matching network to bring the parameter value backwithin range (e.g., altering a variable reactance element to a positionpredetermined to bring the parameter within range).

In other embodiments, rather than (or in addition to) determining that acurrent parameter value is outside a range and therefore requirescorrective action, the matching network can utilize reference values todetermine another characteristic about the plasma chamber. For example,the determination of the characteristic of the plasma chamber may be adetermination that the plasma chamber has reached a particular stage inprocessing a silicon wafer. The stage in processing may be, for example,that etching has reached certain layer of the silicon wafer, or thatdepositing of a layer on the silicon wafer has reached a predeterminedthickness. In these examples, the system, rather than (or in additionto) causing a notice or alarm, may simply cause an action to address thedetermination, such as causing the semiconductor processing to move onto a next stage of processing. In certain embodiments, thecharacterization of the plasma chamber is carried out by analyzingsensor readings (e.g., of output voltage, current, and/or phase) usingFourier transforms at certain frequencies.

The RF matching network and the chamber can further be characterized byinjecting an external signal having a frequency different from thenormal operating frequency of the matching network, the external signalaltering the current value of the parameter, and observe thecharacteristics of the matching network and chamber at this differentfrequency. This different frequency can be a single frequency or a setof multiple frequencies. This external signal can be injected into theRF path during the normal process run or can be injected when the plasmachamber is not running a process. The signal injection can be done atcertain intervals to get a signature of the health of the system and howthe system is varying over a period. This can predict when, for example,the chamber needs cleaning. The injected signal when analyzed can bepost-processed using Fourier transform to determine the chambercharacteristics at specific frequencies. Further, the injected signalcan be used to determine if a certain thickness has been achieved for adeposited layer or if a certain layer has been etched. The externalinjected signal can also be injected at times when non-criticalprocessing is occurring. For example, for a PEALD (Plasma EnhancedAtomic Layer Deposition) type of system, the external signal can beinjected when the actual plasma deposition is not occurring. For asystem that uses level-to-level pulsing (or multi-level pulsing), theexternal signal can be injected during the low power step so the plasmachamber characteristics are developed in real-time.

The above methods may be carried out as part of a method ofmanufacturing a semiconductor. Such a manufacturing method may includeplacing a substrate in the plasma chamber configured to deposit amaterial layer onto the substrate or etch a material layer from thesubstrate, and energizing plasma within the plasma chamber by couplingRF power from the RF source into the plasma chamber to perform adeposition or etching. Further, a matching network using theabove-described method of impedance matching may form part of asemiconductor processing tool (such as tool 86 in FIG. 3), the toolincluding the plasma chamber 19 and the matching network 11A.

Manufacturing Semiconductors Using Artificial Intelligence

Artificial Intelligence (AI) uses machines to mimic human cognitivefunctions. AI can enable a machine to, in a sense, learn, reason, andpredict. As discussed below, AI may be used with semiconductormanufacturing and processing. The system may collect data from one ormore sensors, analyze the data to draw conclusions, and use theknowledge to predict future actions. These tasks may be performed inreal-time to impact the on-going process. But as processes becomecomplex (e.g., more process steps, shorter process time, multiplefrequencies, and multiple power levels), the amount of data collected bya component of the system becomes very large. Collecting and sendingthis large amount of data back to a central CPU for processing anddecision making may be impractical. For a more timely response andbetter results, components of the system may be used to perform localdata analysis and decision making.

A typical RF power delivery system will include an RF generator, cables,sensors, and an RF matching network (sometimes referred to as a“match”). For such an RF power delivery system, the equipment that sitsclosest to the plasma chamber is typically the RF matching network. Allother components of the RF power delivery system are typically isolated,to a degree, from the plasma chamber by the RF matching network. Thus,the RF matching network is an ideal position to collect process data, toanalyze the data, and to make decisions based on the data that improvethe process. Collecting data, learning from the data, and acting on thatdata is not necessarily the exclusive domain of a solid-state RFmatching network using EVCs. Any RF matching network, includingmechanical matching networks, can also collect and process such data.Mechanically variable matching networks are slower to react, however,and thus are less capable of acting on data in real-time.

Prior RF matching networks are basically reactionary with respect totheir control, reacting to changes occurring at their output. Thesematching networks neither anticipate change, nor learn from a process.The AI matching networks discussed below provide significant advantagesin process improvement and repeatability. An AI matching network mayhave several components, including (1) chamber and processcharacterization, (2) known good chamber and process knowledge, (3)predictive tuning to improve process, and (4) data exchange with othercomponents.

In certain embodiments, a Chamber and Process Characterization modeallows the match to be put into a learning mode for a user-definedperiod. In this period, the user runs multiple different types ofrecipes and the match “learns” what is an acceptable process and what isnot. The match also learns what actions to take, to avoid certainchamber limits, such as high output voltage, micro-arcing, etc. Once thelearning period is over, the match uses the knowledge gained during theChamber and Process Characterization mode and applies them to theprocess. This mode is comparable to an autonomous driving car, where thecar is made to learn how to avoid different obstacles by exposing it tothe obstacles and categorizing them as obstacles to avoid. The Chamberand Process Characterization mode allows the match to learn in similarmanner.

In certain embodiments, a Known Good Chamber and Process Knowledge modeallows the match to “learn” what is a known good chamber and process.The match may store multiple data points for a known good chamber andprocess, such as capacitor positions, output voltages, output currents,internal voltages and currents, process durations, tune times, capacitortrajectories, etc. The match then uses this information to comparesubsequent plasma processes and provides notification when a chamberprocess has changed enough that it now represents a change in theprocess. The match may also use the data to predict when a process maybecome out of specification, thus causing chamber maintenance to occurbefore any wafer scrap.

In certain embodiments, a Predictive Tuning to Improve Process algorithmallows the match to predict an end of the etch or deposition process byconstantly analyzing the output data and looking for change in certainbehaviors (such as output frequency spectrum), to predict that an etchor deposition has reached its end. The match may also providesophisticated feedback to the user for in-situ etch or deposited layerthickness by performing chamber analysis during the period when the RFpower is off. This analysis looks for process signature using fastfrequency transforms on signals measured by the match as well asfrequency sweep analysis of the plasma to determine wafer-levelconditions.

The match may also exchange data with other components of the system byproviding and receiving information. This information may be used topredict whether a process is going to change for a component. Forexample, a generator changing its power setpoint can pass thatinformation to the match and the match, in particular a solid statematch working in a multi-level pulsing mode, can pre-start the switchingprocess for faster and more precise tuning.

Data exchange and control can provide significant improvements in waferyield. As an example, a user's goal may be to improve uniformity overthe surface of the wafer. This could be etching uniformity or uniformityof the deposited film. Prior processes control the etch rate ordeposition rate by adjusting the RF power or duration of the process.These power levels and process times have been predetermined based onearlier tests to determine what is acceptable. In the disclosed process,by contrast, the system performs in-situ measurement of the etch ordeposition thickness and allows the system component (e.g., match) tocontrol the power and duration to achieve the desired end result. Theprocess is now more intelligent and adjusts itself with real-time datato produce a wafer that has far tighter uniformity than what apredetermined process could have achieved.

AI provides opportunities for integrated device manufacturers (IDMs),original equipment manufacturers (OEMs), and sub-system suppliers towork together to redefine how the next generation process developmentshould work. Prior processes are based on meeting certain specificationsat each phase gate. IDM's have a process requirement specification basedon what level of on-wafer performance they want to achieve. OEMs in-turndevelop their tool specification and divide it into several portions foreach of the sub-system suppliers. The sub-system suppliers, in turn,then make their own specification that meets what the OEMs are askingfor. Each specification stands alone, though in the end all must worktogether to achieve what the IDM wants. Current design cycle from OEMrequest to providing a beta unit can run 9-12 months and qualificationby the IDM can add another 6 months or more depending upon how manyissues arise during qualification. Therefore, from an IDM's request to aproduct that meets their specification can be roughly be 1.5 years. Thisdevelopment time can be shortened by sharing data between the IDM, OEM,and system component supplier. IDM's process data can be run on theOEM's development tool with a system component supplier's product thathas AI and machine learning capabilities. Chamber instabilities andprocess variations can be characterized well in advance by analyzing thecollected data to map out extents of the acceptable performanceboundary.

Turning now to FIG. 26, the invention may be characterized in certainembodiments as a method 180 of manufacturing a semiconductor. In a firststep (step 181), a semiconductor manufacturing system is operated overtime. This system may be referred to as the “monitored system,” as itwill be monitored to train a learning model. The following descriptionwill refer to the system 86 of FIG. 3, but the invention is not solimited. The monitored system includes an impedance matching network 11Acoupled between an RF source 15 and a plasma chamber 19 at an RF input13 and an RF output 17, respectively. The matching network 11A includestwo EVCs 31A, 33A, but the invention is not so limited. In otherembodiments, the matching network may include any variable reactanceelement (VRE), the VRE having different positions for providingdifferent reactances (such as different capacitances or inductances).

In another step (step 182), the method 180 receives first values for aparameter of the monitored system, the first values comprising differentvalues for the parameter over the time period of operation of themonitored system. This parameter may be any parameter associated withthe system 86, such as one or more of a current position of the VRE fromamong the possible positions of the VRE; a load impedance at an RFoutput of the matching network or at a node internal to the matchingnetwork; a matching tune time; a reflected RF power or a reflectioncoefficient (input gamma) at an RF input of the matching network; apeak-to-peak voltage at an RF output of the matching network; a DCvoltage at an RF output, input, or internal to the matching network; aDC current at an RF output, input, or internal to the matching network;and/or a phase angle of the load impedance at an RF output of thematching network. In other embodiments, the parameter may be related toa component other than the matching network, such as a parameter of theRF source (e.g., a power setpoint) or of the plasma chamber. It is alsonoted that, rather than collecting values for only one parameter, themethod may collect values for a plurality of parameters.

In another step (step 183), a learning model is trained using the firstvalues for the parameter. The machine learning model may be any modelbuilt by machine learning algorithms based on sample or training data.The model can “learn” based on the training data (first values) it isprovided. The machine learning model may be supervised or unsupervised.

The training of the learning model may occur in a variety of ways. Inone embodiment, the training of the learning model comprises thelearning model determining a valid range of values for the parameterbased on the received first values for the monitored system. Forexample, the valid range of values may be based on values for themonitored system determined over the time period of operation for anamount of current drawn by each of a plurality of switches of the VRE ofthe monitored system, the VRE being electronically variable; an amountof current drawn by at least one fan of the matching network of themonitored system; a number of switching operations by each of aplurality of switches of the VRE of the monitored system, the VRE beingelectronically variable; a number of motor reversals and a duration ofeach motor operation for a motor of the matching network of themonitored system, the VRE being mechanically variable using the motor;an amount of DC or AC current drawn from an input power supply of themonitored system; and/or an AC or DC voltage at a point inside thematching network of the monitored system. In other embodiments, ratherthan learning a valid range of values for a parameter, the training maylearn to associate certain parameters values with other characteristicsof the system, such as a problem with a component (e.g., the chamber), aneed for a component to be serviced (e.g., a need for the chamber to becleaned), or the reaching or completion of a stage in processing (e.g.,that etching of a certain layer is complete, or that depositing a layeron a wafer has reached completion). It is noted that, after the initialtraining process, current values of a parameter may be provided to thelearning model to continue the training of the learning model.

In another step (step 184), a substrate is placed in a plasma chamber ofa controlled semiconductor manufacturing system (controlled system), theplasma chamber depositing a material layer onto the substrate or etchinga material layer from the substrate. The controlled system includes animpedance matching network coupled between an RF source and the plasmachamber, the matching network of the controlled system comprising a VREhaving different positions for providing different reactances (see,e.g., FIG. 3). In certain embodiments, the monitored system and thecontrolled system are the same system, while in other embodiments theyare not. Further, the controlled system may form part of a plurality ofcontrolled systems each controlled using the trained learning model.Thus, the trained learning model can be used for more than onecontrolled system. Further, the controlled systems may or may notinclude the monitored system.

In another step (step 185), based on a sensor signal (or other receivedsignal, such as a signal from the RF source or plasma chamber), acurrent value of the parameter for the controlled system is determined.Further, using this current value of the parameter and the trainedlearning model, a characteristic of the controlled system is determined(step 186). As discussed above, in one embodiment, the training of thelearning model comprises the learning model determining a valid range ofvalues for the parameter based on the received first values for themonitored system. In such embodiments, the determination of thecharacteristic of the plasma chamber of the controlled system may bebased on a determination that the current value is outside the validrange of values, though the invention is not so limited.

The determined characteristic may be any characteristic of thecontrolled system or any of the system's components. For example, thedetermined characteristic may be that there is a problem with the plasmachamber, that the plasma chamber needs to be cleaned, or that the plasmachamber has reached a particular stage in processing a silicon wafer.The determined characteristic may also be a characteristic of the RFsource or the matching network.

In certain embodiments, the learning model receives the current value ofthe parameter and determines the characteristic of the system. In otherembodiments, rather than the learning model itself determining thecharacteristic, the learning model may provide certain outputs that arethen used to determine the characteristic.

Returning to FIG. 26, once the characteristic of the system isdetermined, an action is taken (step 187) upon the controlled system toaddress the determined characteristic. For example, if the determinedcharacteristic is that the parameter is out of an acceptable range, theaction taken could be an action to bring the parameter back into theacceptable range, such as adjusting one of the components of the system.For example, the action may be to adjust the position(s) of the one ormore VREs to return the value of the parameter to the proper range. Inone embodiment, for each of the first values of the parameter, acorresponding VRE position is determined, and these VRE positions andtheir relationship to the first values are used to further train thelearning model. In this manner, the training of the learning model mayinclude the learning model learning a valid range of values for theparameter based on the received first values, and learning which of theVRE positions for the monitored system will cause the parameter toreturn to the valid range of values. Further, using the learning modeland the current value of the parameter, the learning model can determinea new position for the VRE that will return the parameter of themonitored system to the valid range of values.

In other embodiments, returning the parameter to a predetermined rangemay be carried out by other means. Broadly speaking, for each of thefirst values of the parameter, the system may receive a correspondingsecond value for a second parameter, and the learning model may befurther trained using the second values and their correspondence withthe first values. The action taken may be to alter, using the learningmodel and the current value of the parameter, the second parameter ofthe controlled system to a new value determined by the learning model toreturn the parameter of the monitored system to the valid range ofvalues.

The action taken is not limited returning to the current parameter to apredetermined range. AI can be used to treat a variety of problems, andthe action may include a notice or alarm (visual, audible, on a displayscreen, sent via a message or email, etc.). For example, the determinedcharacteristic could be that there is a problem with the plasma chamber.The action taken may be to initiate a process to fix the problem, tostop a process until the problem is fixed, and/or or to notify a user ofthe problem. The determined characteristic could also be that the plasmachamber needs to be cleaned. The action taken could be to initiate acleaning process, to stop a process until the chamber is cleaned, and/oror to notify a user of the need to clean the chamber. The determinedcharacteristic could also be that the plasma chamber has reached aparticular stage in processing a silicon wafer. The action taken couldbe to initiate a new stage of the wafer processing and/or to providenotice of the current stage in processing. It should be understood thatthe foregoing are just examples and the invention is not so limited.

In one embodiment, the parameter is a power setpoint of the RF source,and the determined characteristic is a change in the power setpoint. Thecontrolled system includes a VRE that is electronically variable suchthat its reactance is varied by switches carrying out the switchingprocess (see, e.g., the EVCs of FIG. 3). The action taken upon thecontrolled system is starting a switching process for the VRE. Forexample, as discussed above, an RF source (e.g., generator) can passinformation to the match that the RF source is changing its powersetpoint so that the match can pre-start its switching process forfaster and more precise tuning.

In another embodiment, the determined characteristic of the controlledsystem comprises a determination that etching in the plasma chamber hasreached certain layer of a silicon wafer, and the action taken comprisesstopping etching. The determined characteristic may further comprise adetermination that depositing of a layer on a silicon wafer in theplasma chamber has reached a predetermined thickness, and the actiontaken may further comprise stopping deposition of the layer.

The foregoing steps for applying AI to semiconductor manufacturing andprocessing can be carried out by one or more processors. For example, ifthe matching network is carrying out one or more of the foregoing steps,the control circuit (e.g., control circuit 45) of the matching networkmay carry out the steps. In this embodiment, the control circuit couldreceive the first values for the parameter, train the learning model,determine the current value of the parameter, determine thecharacteristic of the system, and cause the action to be performed. Incertain embodiments where the monitored system is different from thecontrolled system, the matching networks of the respective systems canperform different functions. For example, the receiving of the firstvalues may be performed by the matching network of the monitored system,while the steps of determining a current value of the parameter anddetermining a characteristic based thereon are performed by the matchingnetwork of the controlled system. The invention is not limited to thematching network performing all or any of these steps, however, as othercomponents of the semiconductor manufacturing system can carry out theAI operations. Further, AI operations may be carried out by a unitseparate or remote from the manufacturing system. For example, data maybe provided to a remote system that performs AI analysis (e.g., traininga learning model) and/or determines the current characteristic. Further,the invention may be understood as a non-transitory computer-readablestorage medium encoded with instructions which, when executed on aprocessor, perform the disclosed method, the instructions being storedon any component of the system or systems, or outside the systems.

Coordinated Operation of RF Source and Matching Network

RF amplifiers, RF generators, and matching networks are used in manyapplications, including telecommunication, broadcast, and industrialprocessing. In the following embodiments, the term RF generator is usedto represent a system comprising of an RF amplifier and a DC powersupply. An RF generator may be understood as a type of RF source, thoughan RF source is not limited to the exemplified RF generator.

As discussed below, the operation of the RF generator may be coordinatedwith the operation of an RF impedance matching network. In a preferredembodiment, the matching network is an RF solid-state matching networkthat uses solid-state elements (e.g., EVCs), instead ofelectro-mechanical elements, to tune the impedances. The combined RFgenerator and matching network can be in one mechanical enclosure or canbe in two separate enclosures. Both the RF generator and the matchingnetwork can be air cooled or water cooled or a combination of both.

In an RF generator, an RF signal is taken at the input of the RFamplifier and this RF signal is used to modulate the power derived fromthe DC power supply in order to provide RF power at significantly higherpower than the input. Commonly-owned U.S. Pat. No. 9,345,122 isincorporated herein by reference in its entirety. Most RF generatorsused in semiconductor processing maintain a stable output impedance.This output impedance is typically 50 Ohm. In a typical RF system, theoutput of the RF generator is then connected to the input of the RFmatching network (see, e.g., FIG. 3) either directly, or through a 50Ohm coaxial cable. FIG. 1 shows the typical connection of an RFgenerator (RF source 15) to a matching network 11, which is connected toa load (plasma chamber 19).

The matching network is configured to maintain an input impedance thatmatches the characteristic impedance of the coaxial cable and the outputimpedance of the RF generator. Since in most cases that impedance is 50Ohm (i.e., 50+j0) or very close to that value, the matching network isdesigned to transform the load impedance to 50 Ohm.

Exemplary RF Generator

FIG. 27 is a block diagram of an example RF generator 60. The RFgenerator is coupled to a plasma chamber 19 through a matching network11A. The RF generator 60 comprises an RF amplifier 61 and a DC powersupply 62. The RF amplifier 61 has an RF input 64, a DC input 66, and anRF output 65. An RF signal source 63 provides an RF signal to the RFamplifier 61 at the RF input 64. A DC source 62 provides a DC voltage tothe RF amplifier 61 at the DC input 66. The RF signal can modulate thepower received at the DC input 66 to provide an RF output power at theRF output 65 that is higher than the power at the RF input 64. The RFsignal source can be any device capable of providing a sufficient RFsignal for operation of an RF generator, and the DC source can be anydevice capable of providing a sufficient DC signal for operation of anRF generator.

The exemplified RF generator also includes sensors 57, 58 for measuringa parameter (e.g., a voltage, a current, and/or a phase angle betweenthe voltage and current), though these particular sensors in theseparticular locations are not required. Sensor 58 is connected to the RFoutput 65 to detect an RF output parameter. Sensor 57 is connected tothe DC source 62. This sensor is configured to detect a DC inputparameter.

The RF generator 60 further includes a control unit 67 that can becoupled to the various components of the RF generator 60. The controlunit 67 can provide several functions for the RF generator 60. Thecontrol unit 67 can receive instructions from a user or a system at aninput 56. The control unit 67 can receive the RF output parameter fromsensor 65 as part of control loop 68. The control unit 67 can use the RFoutput parameter to determine the RF output power and/or to control theDC source 62 and/or the RF signal source 63. Further, the control unit67 can receive the DC input parameter from sensor 57 and determine theDC input power.

RF Generator-Matching Network Communication

In a typical RF generator-matching network system, there is noinformation sharing between the RF generator and the matching network.The RF generator supplies the RF power and the matching network ensuresthat maximum amount of that power is delivered to the load. Each has itsown control circuitry to provide local control. Problems arise whenthere is a change in the load impedance. This change can be a slowchange or a sudden change. In response to this change in the loadimpedance, the matching network's control circuitry calculates theconditions (e.g., new capacitor positions) that would continue totransform this new load impedance to 50 Ohm at its input. In doing so,the matching network may switch certain reactive elements (e.g.,capacitors) ON or OFF. This switching is done very quickly, in typically10 usec to 200 usec. This fast switching creates a sudden impedancechange at the input of the matching network which is seen by the outputof the RF generator as a sudden load change. The RF generator's controlcircuit has control schemes for delivering a set amount of power to itsoutput as well as control schemes for protecting the RF generator fromexcessive stress, such as excessive power dissipation, high reflectedpower, excessive voltage on internal components, or excessive currentthrough internal components. These control loops can be carried outusing hardware and/or software.

Since in a typical system there is no communication between the RFgenerator and the matching network, the RF generator's control circuitis unaware that an impedance change is about to occur at its output andtherefore its loop response is not limited and can over or undercompensate, resulting in power spikes at its output. FIG. 28 shows anexample transient response 50 of an RF generator. The figure shows 4transient conditions 55A-D that exist each time the matching networkreactance switches. Traces 51, 52 are the matching network reactanceelement conditions. Trace 53 is the RF generator forward power, andTrace 54 is the measured reflected power. As can be seen, at thebeginning of each reactance step in the matching network, the RFgenerator shows a transient spike in the forward power (trace 53). Thematching network then in turn sees the power change at its input, andthis results in a transient change in the load impedance, and thereforethe matching network reacts to this transient. If the RF generator wasaware that the matching network was going to switch, the RF generatorcould temporarily change the speed of its response, so that the forwardpower transient is limited. The advantage with this communication fromthe matching network to the RF generator would be to limit thetransients from the RF generator and allow for a faster tune time.

FIG. 29 is a flow chart of a method 190 of matching an impedanceaccording to one embodiment using the proposed scheme. A matchingnetwork is coupled between an RF source (in the preferred embodiment, anRF generator as described herein) and a plasma chamber (operation 191).Referring to exemplary FIG. 3, the matching network 11A comprises an RFinput 13 configured to operably couple to the RF source 13, an RF output17 configured to operably couple to the plasma chamber 19, and at leastone variable reactance element (VRE) (e.g., EVCs 33A and 31A), the VREhaving different positions for providing different reactances. The RFsource 15 is configured to provide an RF signal to the RF input 13 ofthe matching network, the RF source 15 comprising an RF source controlcircuit 16 (see also exemplary control circuit 67 of FIG. 27) configuredto carry out a power control scheme to control a power delivered to theRF input 13 of the matching network. For the avoidance of doubt, theinvention is not limited to the embodiments shown in the figures.

Next, a parameter is determined that is related to the matching networkor plasma chamber (operation 192). As will be described below, thisparameter may be, for example, a voltage, a current, a phase, a matchingnetwork output impedance, or a matching network input impedance.

Next, based on the determined parameter, the system determines (from thedifferent positions of the VRE) a new position for the VRE to reduce areflected power at the RF input of the matching network (operation 193).A variety of exemplary methods for determining a new VRE (e.g., EVC)position are discussed above. Note that the matching network may includemore than one VRE, as is shown in FIGS. 2 and 3. In these cases, the“different positions for the VRE” can refer to different combinedpositions for the VREs of the matching network. For example, if thereare two VREs, then determining a new position for the VRE can includedetermining a new position for the first VRE and determining a newposition for the second VRE.

Further, the matching network provides a notice signal to the RF sourceindicating the VRE will be altered (operation 194), and, in response,the RF source control circuit alters the power control scheme (operation195). The different methods for altering the power control scheme (suchas dampening the control loop) are described below. While the powercontrol scheme is altered, the VRE is altered to the new position(operation 196). As discussed above, by altering the power controlscheme when the VRE is being altered, the system the RF generator wouldbe to limit the transients from the RF generator and allow for a fastertune time. Eventually, the power control scheme may be returned to itsprior un-altered state (operation 197). Further, the method 190 may onceagain determine the parameter (operation 197). In the exemplifiedembodiment, the parameter is not once again determined until the powercontrol scheme returns to the prior un-altered state, but the inventionis not so limited. For example, the parameter may be re-determinedbefore the power control scheme returns to the un-altered state.

According to the method described, when the matching network 11A detectsa change at its output 17 that requires a change in the reactiveelements (e.g., capacitors 33A, 31A), the matching network controlcircuit (e.g., control circuit 45 of FIG. 3) can send a signal to the RFgenerator, via a signal connection between the two, and in response theRF generator can alter its power control scheme. In a preferredembodiment, the alteration of the power control scheme will be adampening of the control loop response. The dampening of a control loopcan take many forms. For example, dampening can comprise reducing a gainof the RF generator or a gain of a control loop of the control circuit.The alteration of the gain may be accomplished, for example, by alteringa gain provided by one or more amplifiers of the RF generator. Thedampening of the control loop may also comprise pausing the powercontrol scheme such that the RF signal is maintained at a current poweroutput (thus making the gain 0). In certain embodiments, the alterationor dampening is carried out for a predetermined period of time (e.g.,200 microseconds), which can be pre-programed into the RF generatorbased on the matching network switching characteristics. In otherembodiments, the duration of the alteration can vary depending ondifferent factors discussed below.

There are yet other methods of altering the power control scheme. Incertain embodiments, upon receiving a notice signal from the matchingnetwork, the RF generator can alter the power control scheme of the RFgenerator by altering the power setpoint of the RF generator to changethe power delivered by the RF source to the RF input of the matchingnetwork. This may be done, for example, if a deposited film thickness ischanging. The RF source may be configured to receive from the matchingnetwork a signal indicative of a DC voltage of a wafer chuck configuredto hold a wafer in the plasma chamber (see, e.g., electrode 23 or 25 ofFIG. 1), the DC voltage being indicative of a deposited film thickness.The power setpoint may be altered in response to the signal indicativeof the DC voltage of the chuck to correct the problem of the changingfilm thickness.

The notice signal may be further indicative of a duration of time.Further, the alteration of the power control scheme may be carried outfor the duration of time indicated by the notice signal.

In another embodiment, the RF generator will determine the duration ofthe dampening of the response based on the measurement RF generator doesat its output. The RF generator will remove the temporary dampening ofthe control loop response once it sees that the load impedance at itsoutput is stable and the matching network has the load impedance tunedto within the acceptable reflected coefficient.

In another embodiment, the matching network will provide two signals tothe RF generator, one that indicates that the matching network is aboutto switch the reactive elements and a second signal (sometimes referredto as an “information signal”) to indicate the magnitude of change inthe reactive elements. The RF generator will then use the second signal(the information signal) to determine how much to dampen the controlloop response. Thus, the extent of the dampening (e.g., the reduction ofthe gain of the RF source) may be based on the information signal.Further, or alternatively, the duration of the alteration of the powercontrol scheme may be based on the information signal. In certainembodiments, the information signal may form part of the notice signal.

Other signals may be communicated between the RF generator and thematching network, such as those indicative of the voltage, current,and/or phase angle between the voltage and current. For example, whereall three are communicated, the RF generator may have a voltage andcurrent sampling sensor at its output. This sensor (the VI sensor),samples the voltage and current at the output of the RF generator andsends those signals to the RF generator control circuit. The RFgenerator control circuit then converts these signals to equivalent DClevel signals and determines the phase angle between the two signals. Itthen sends these three signals, voltage, current, and phase, to thematching network. The matching network uses this information in itscontrol algorithm to determine, for example, the load impedance andcontrol the reactive elements of the matching network accordingly. Theadvantage of this method is that there is only one VI sensor needed andit reduces the cost of the overall system. The second advantage is thatthe common VI sensor reduces the chances of the matching network or theRF generator sensor determining different V, I, and phase values. Thisdifference can occur if the RF generator is located at a distance fromthe generator and is connected to the matching network via a coaxialcable. Any small variations from the nominal 50 Ohm match conditions atthe input of the matching network can get transformed by the longcoaxial cable and show up as a higher reflected power. This results inthe RF generator showing a higher reflected power, while the matchingnetwork shows a low reflected power. The common sensor at the output ofthe RF generator need not be a VI sensor. It can alternatively be aphase/mag sensor, or a forward/reflected power sensor. Accordingly, thedata transmitted from the RF generator to the matching network can alsodifferent.

In another embodiment, the sensor can be located at the output of thematching network. The matching network then uses the load informationgathered from this output sensor and its knowledge of its currentreactive element positions and calculate the impedance at the matchingnetwork's input. It then provides that input to the RF generator, sothat the RF generator can use it to control the power that is deliveredto the input of the matching network.

Another signal that can be provided by the RF generator to the matchingnetwork is a signal indicative of the frequency of operation, the RFfrequency. The matching network can use that frequency information todetermine the impedance of different reactive elements in its circuitry.Those reactive impedance values can then be used by the matching networkin its control algorithm to control the tuning as well as forcalculation of voltages and currents across certain reactive elementsfor protective purposes.

In another embodiment, the RF generator and the matching network can bein one enclosure, with the RF generator controlling the frequency ofoperation and the matching network using one reactive element to varythe impedance transformation from its output to its input. In this case,the RF generator and the matching network combined make up the full RFsystem capable of both providing the required power to the load as wellas matching the load so that maximum power is being transferred from theRF generator to the load.

The RF generator and the matching network can also have a common controlboard, where all control decisions for the two are taken. This reducesthe circuit redundancy which can help in reducing the material cost ofboth the RF generator and the matching network as well as reducing thesize of each box. The RF generator and the matching network can also bein one enclosure to further enable a compact low-cost design.

Other signals that can be shared between the RF generator and thematching network are any transient signals detected by the matchingnetwork at its output. The matching network can have an output sensorthat can detect either voltage, current, or phase, or any combination ofthe three. These sensors can detect transient changes occurring in theload. For the case where the RF generator and the matching network areused in a system to match the variable load of a plasma chamber to theRF generator, the matching network sensors can detect plasma transients,such as micro-arcing, and then provide that information to the RFgenerator. RF generator can then alter its power to extinguish themicro-arc.

In another embodiment, the matching network can measure the DC voltageat its output and correlate the DC voltage to a certain load condition.In the case of the RF generator and the matching network being used in asemiconductor processing tool, the DC voltage may indicate that theprocess is changing and the compensation for that process change couldbe the change in the forward power from the RF generator. Thus, acombined RF generator and matching network can compensate for processchanges that occur over a period and automatically correct the on-waferresults by compensating the RF generator power.

It is understood that the methods described above may be incorporatedinto a system comprising an RF source and a matching network asdiscussed herein. The system may further include a plasma chamber toform a semiconductor manufacturing system. The methods described abovemay also be incorporated into a method of manufacturing a semiconductor,where a substrate is placed in a plasma chamber configured to deposit amaterial layer onto the substrate or etch a material layer from thesubstrate. This application incorporates by reference in its entiretycommonly-owned U.S. Pat. No. 10,460,912, U.S. Pat. Pub. No.2020/0083022, and U.S. Pat. Pub. No. 2019/0267212.

Resonant Filter for Switching Circuit of EVC

As discussed above, for example, with regard to FIG. 16, EVCs may usePIN or NIP diodes as an electronic switch. The PIN diode is forwardbiased or reverse biased to turn it ON or OFF, respectively. In theexemplified embodiment of FIG. 16, the first power switch 611A and thesecond power switch 613A switch in a complementary manner. That is, whenthe first switch 611A is open, the second switch 613A is closed, andwhen the first switch 611A is closed, the second switch 613A is open.The biasing power supplies 615A, 617A bias the PIN diode to turn ON orOFF, as needed. When this PIN diode switch is used in an RF circuit asan RF switch, an RF voltage exists on the cathode side of the PIN diode(node 668A of FIG. 16) whenever the PIN diode is in OFF state. Note thatthe PIN diode can be configured such that its cathode is grounded andits anode is connected to the capacitor 653A and filter 641A. Also, theswitching circuit 640A can also be implemented with NIP diodes which areopposite in polarity to PIN diodes.

Whenever an RF voltage exists on node 668A, that RF voltage is blockedfrom going towards the first and second power switches 611A, 613A. If ablocking circuit is not installed, the RF voltage will be imposed onfirst and second power switches 611A, 613A and thus short into thebiasing voltage supplies. This is undesirable. Therefore, the filter641A of the PIN diode switching circuit is typically an inductor havinga sufficiently high value inductance such that it blocks the RF voltagefrom appearing at the driver circuit output 607A.

While using an inductor as the filter 641A is sufficient to be used forblocking the RF voltage, it has a downside. Large Inductors store energyand when the biasing driver circuit 639A switches between the ON to OFFor OFF to ON state, the current flowing in the inductor 641A abruptlystops or starts. This sudden change in current results in development ofa voltage across the inductor 641A, according to the following formula:

$v = {L\frac{di}{dt}}$

where L is the inductance of the inductor, di/dt is the change incurrent for the change in time (the slope of the current when it isplotted against time). As seen from this formula, the larger the valueof the inductor, the larger this voltage is. This voltage then appearsacross the PIN diode and can exceed the breakdown voltage of the PINdiode and damage it. One solution to overcome this large build-up ofvoltage is to slow down the switching of the first and second powerswitches 611A, 613A such that the change in current occurs more slowly.The downside of this slow switching is that the switching loss in thefirst and second power switches 611A, 613A goes up and can exceed thesafe operating area of the devices used in the first and second powerswitches 611A, 613A.

Note that sometimes a capacitor to ground from the output 607A is alsoused in conjunction with the filter 641A. The purpose of this capacitoris to provide a path to ground for whatever RF voltage remains after itpasses through the inductor.

FIG. 30 provides a new filter 741A for a switching circuit 740A of anEVC. FIG. 30 is similar to FIG. 16, with its primary difference beingfilter 741A. It is noted that, insofar as components in FIG. 30 usereference numbers similar to those in FIG. 16, the components and theirpotential alternatives are similar to those described in FIG. 16.

In FIG. 30, rather than using an inductor, parallel resonant filter 741A(comprising capacitor 743A positioned parallel to inductor 742A) is usedso that the blocking impedance of the filter 741A remains high withrespect to the RF frequency. In this embodiment, the parallel resonantfilter 741A continues to block the RF voltage from appearing at output607A, while at the same time allowing the use of a lower inductancevalue inductor 742A in the parallel resonant filter so that the energystored in the inductor 742A is low and the voltage developed across theinductor 742A at the time of the switching is also low.

The advantage of this type of filter circuit 741A is that it allows theswitch to be switched quickly, but still keeps the voltage across thePIN diode under the breakdown voltage of the PIN diode. The fastswitching of the first and second power switches 611A, 613A reduces theswitching loss and improves the reliability of the driver circuit 639A.

It is noted that the parallel resonant filter circuit 741A and the othercomponents of the switching circuit 740A are just one example of theinvention, and there could be several modifications to this topology andcomponent configurations. For example, the PIN diodes may be NIP diodes.Further, the diode may be flipped such that its anode is connected tonode 668A. Further, the forward and reverse biasing voltages 615A, 617Acan be reversed. Further, resistor 744 may or may not be included. Aresistor, such as resistor 744, can be installed in series with theinductor 742A to control the amount of forward biasing current. Further,the location of the resistor for controlling the forward biasing currentcan be in series with the switch connected to the forward biasingvoltage. Further, the inductor may be selected such that it has aparallel resonance at the operating frequency due to self-capacitance.In that case, a separate external capacitor may not be needed. It isfurther noted that switching circuit 740B is a similar to switchingcircuit 740A but is used for switching diode 653B (rather than diode653A) and does not show the details of the driver circuit 639B (as isshown for driver circuit 639A). As with FIG. 16, the components ofdriver circuit 639A may be used for each of the fixed capacitors of EVC651.

It is noted that, generally, it would be preferable to use a single highimpedance, such as an inductor, for filter 741A, rather than a resonantcircuit. There are several reasons for this. First, resonant circuitsare highly tuned to a specific frequency and, due to componenttolerances or manufacturing variations, the resonant frequency can shiftand thus make the resonant circuit not very effective. Further, a singlehigh impedance circuit, such as an inductor, is broad band and itsblocking characteristics are not very sensitive to tolerance ormanufacturing variations. Further, a resonant circuit adds additionalcost, as it is now two components and both components have to be verytight tolerance, which further drives up the cost. Further, resonantcircuits have a circulating current that flows within the two componentsthat make up the resonant circuit, and this circulating current addsadditional thermal dissipation which needs to be removed and adds morecomplexity to the circuit. Thus, a resonant circuit adds more complexityand cost.

The more obvious solution to the voltage spike across the PIN diode isto slow down the ON/OFF transition since, as shown in the voltageequation above, increasing dt will cause the voltage to drop withoutadding the complexity and cost of using a resonant filter. But there aredownsides to slowing the ON/OFF transition, including causing moreswitching loss in the PIN diode. The resonant filter, while not the mostobvious solution in view of the foregoing, is the solution that willsolve the voltage spike problem without causing switching loss in thePIN diode. The resonant filter is especially helpful in matchingnetworks using multi-level power setpoints, such as those embodimentsdiscussed with respect to FIGS. 14-15. In these embodiments, fastswitching is required, and slowing the ON/OFF transition is not asuitable solution for the filter. For example, the resonant filter maybe especially beneficial where the switching time was less than 100microseconds, or less than 50 microseconds, or less than 200microseconds.

While the embodiments of a matching network discussed herein have used Lor pi configurations, it is noted that he claimed matching network maybe configured in other matching network configurations, such as a ‘T’type configuration. Unless stated otherwise, the variable capacitors,switching circuits, and methods discussed herein may be used with anyconfiguration appropriate for an RF impedance matching network.

While the embodiments discussed herein use one or more variablecapacitors in a matching network to achieve an impedance match, it isnoted that any variable reactance element can be used. A variablereactance element can include one or more discrete reactance elements,where a reactance element is a capacitor or inductor or similar reactivedevice.

While the inventions have been described with respect to specificexamples including presently preferred modes of carrying out theinvention, those skilled in the art will appreciate that there arenumerous variations and permutations of the above described systems andtechniques. It is to be understood that other embodiments may beutilized and structural and functional modifications may be made withoutdeparting from the scope of the present inventions. Thus, the spirit andscope of the inventions should be construed broadly as set forth in theappended claims.

What is claimed is:
 1. A radio frequency (RF) impedance matching circuitcomprising: an RF input configured to operably couple to an RF sourceproviding an RF signal; an RF output configured to operably couple to aplasma chamber; at least one electronically variable capacitor (EVC)comprising discrete fixed capacitors, each fixed capacitor of each EVChaving a corresponding switching circuit for switching in and out thefixed capacitor to alter a total capacitance of the EVC; and a controlcircuit configured to cause the switching in and out of the fixedcapacitors of each EVC to enable an impedance match; wherein eachswitching circuit for each fixed capacitor of each EVC comprises: adiode operably coupled to the fixed capacitor to cause the switching inand out of the fixed capacitor, the diode being a PIN diode or an NIPdiode; a driver circuit operably coupled to the diode; and a resonantfilter positioned between the driver circuit and the diode, the resonantfilter comprising an inductor and a capacitor coupled in parallel. 2.The matching circuit of claim 1 wherein each EVC is configured suchthat, when any of the fixed capacitors switches out, the switchingoccurs in 100 microseconds or less.
 3. The matching circuit of claim 1wherein each EVC is configured such that, when any of the fixedcapacitors switches out, the switching occurs in 200 microseconds orless.
 4. The matching circuit of claim 1 wherein the RF source isconfigured to provide at least two repeating, non-zero pulse levels. 5.The matching circuit of claim 4: wherein, by the switching in or out ofthe fixed capacitors, each EVC is configured to switch between aplurality of match configurations for enabling the impedance match andthereby reducing a reflected power at an output of the RF source as thevariable impedance of the plasma chamber changes; and wherein, for eachof the pulse levels, the control circuit is configured to determine,from the plurality of match configurations, a new match configuration toenable the impedance match.
 6. The matching circuit of claim 1 whereinthe driver circuit comprises: a first power switch receiving a reversebias voltage and configured to switchably connect the reverse biasvoltage to a common output in response to a received input signal; and asecond power switch receiving a forward bias voltage and configured toswitchably connect the forward bias voltage to the common output inresponse to a received input signal; wherein a first terminal of theresonant filter is electrically coupled to the common output; andwherein a second terminal of the resonant filter, distinct from thefirst terminal of the resonant filter, is electrically coupled to a nodebetween the fixed capacitor and the diode.
 7. The matching circuit ofclaim 6 wherein to switch the switching circuit ON and thereby switch inthe corresponding fixed capacitor, a DC current flows from the forwardbias voltage through the diode.
 8. The matching circuit of claim 7wherein the forward bias voltage and the diode are coupled to a commonground.
 9. A method of matching an impedance comprising: coupling aradio frequency (RF) input of a matching circuit to an RF source;coupling an RF output of the matching circuit to a plasma chamber,wherein the matching circuit comprises: at least one electronicallyvariable capacitor (EVC) comprising discrete fixed capacitors, eachfixed capacitor of each EVC having a corresponding switching circuit forswitching in and out the fixed capacitor to alter a total capacitance ofthe EVC; and a control circuit configured to cause the switching in andout of the fixed capacitors of each EVC to enable an impedance match;wherein each switching circuit for each fixed capacitor of each EVCcomprises: a diode operably coupled to the fixed capacitor to cause theswitching in and out of the fixed capacitor, the diode being a PIN diodeor an NIP diode; a driver circuit operably coupled to the diode; and aresonant filter positioned between the driver circuit and the diode, theresonant filter comprising an inductor and a capacitor coupled inparallel; and matching an impedance by at least one of the switchingcircuits of the at least one EVC switching in or out its correspondingfixed capacitor to alter a total capacitance of the EVC.
 10. The methodof claim 1 wherein each EVC is configured such that, when any of thefixed capacitors switches out, the switching occurs in 100 microsecondsor less.
 11. The method of claim 1 wherein each EVC is configured suchthat, when any of the fixed capacitors switches out, the switchingoccurs in 200 microseconds or less.
 12. The method of claim 1 whereinthe RF source is configured to provide at least two repeating, non-zeropulse levels.
 13. The method of claim 12: wherein, by the switching inor out of the fixed capacitors, each EVC is configured to switch betweena plurality of match configurations for enabling the impedance match andthereby reducing a reflected power at an output of the RF source as thevariable impedance of the plasma chamber changes; and wherein, for eachof the pulse levels, the control circuit is configured to determine,from the plurality of match configurations, a new match configuration toenable the impedance match.
 14. The method of claim 1 wherein the drivercircuit comprises: a first power switch receiving a reverse bias voltageand configured to switchably connect the reverse bias voltage to acommon output in response to a received input signal; and a second powerswitch receiving a forward bias voltage and configured to switchablyconnect the forward bias voltage to the common output in response to areceived input signal; wherein a first terminal of the resonant filteris electrically coupled to the common output; and wherein a secondterminal of the resonant filter, distinct from the first terminal of theresonant filter, is electrically coupled to a node between the fixedcapacitor and the diode.
 15. The method of claim 14 wherein to switchthe switching circuit ON and thereby switch in the corresponding fixedcapacitor, a DC current flows from the forward bias voltage through thediode.
 16. The method of claim 15 wherein the forward bias voltage andthe diode are coupled to a common ground.
 17. A semiconductor processingtool comprising: a plasma chamber configured to deposit a material ontoa substrate or etch a material from the substrate; and an impedancematching circuit operably coupled to the plasma chamber, the matchingcircuit comprising: an RF input configured to operably couple to an RFsource providing an RF signal; an RF output configured to operablycouple to the plasma chamber; at least one electronically variablecapacitor (EVC) comprising discrete fixed capacitors, each fixedcapacitor of each EVC having a corresponding switching circuit forswitching in and out the fixed capacitor to alter a total capacitance ofthe EVC; and a control circuit configured to cause the switching in andout of the fixed capacitors of each EVC to enable an impedance match;wherein each switching circuit for each fixed capacitor of each EVCcomprises: a diode operably coupled to the fixed capacitor to cause theswitching in and out of the fixed capacitor, the diode being a PIN diodeor an NIP diode; a driver circuit operably coupled to the diode; and aresonant filter positioned between the driver circuit and the diode, theresonant filter comprising an inductor and a capacitor coupled inparallel.
 18. The processing tool of claim 1 wherein each EVC isconfigured such that, when any of the fixed capacitors switches out, theswitching occurs in 100 microseconds or less.
 19. The processing tool ofclaim 1 wherein each EVC is configured such that, when any of the fixedcapacitors switches out, the switching occurs in 200 microseconds orless.
 20. A method of fabricating a semiconductor, the methodcomprising: placing a substrate in a plasma chamber configured todeposit a material layer on the substrate or etch a material layer fromthe substrate; energizing plasma within the plasma chamber by couplingRF power from an RF source to the plasma chamber to perform thedeposition or etching; and while energizing the plasma, carrying out animpedance match by an impedance matching circuit coupled between theplasma chamber and the RF source, the matching circuit comprising: an RFinput configured to operably couple to the RF source; an RF outputconfigured to operably couple to the plasma chamber; at least oneelectronically variable capacitor (EVC) comprising discrete fixedcapacitors, each fixed capacitor of each EVC having a correspondingswitching circuit for switching in and out the fixed capacitor to altera total capacitance of the EVC; and a control circuit configured tocause the switching in and out of the fixed capacitors of each EVC toenable an impedance match; wherein each switching circuit for each fixedcapacitor of each EVC comprises: a diode operably coupled to the fixedcapacitor to cause the switching in and out of the fixed capacitor, thediode being a PIN diode or an NIP diode; a driver circuit operablycoupled to the diode; and a resonant filter positioned between thedriver circuit and the diode, the resonant filter comprising an inductorand a capacitor coupled in parallel.